## when to assume x is insignificant

Cristian Cortes 1L
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### when to assume x is insignificant

For some questions on sampling week 2, where we would have a number like .032-x and equal it to Kb for an example, when is it fine or restricted to assume x is so insignifcant we can keep it out?

John Antowan 1K
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### Re: when to assume x is insignificant

I usually use the given equlibrium constant as a bit of a guess. If it is below 1x10^-4, I usually would estimate x is insignificant just to be safe, but I believe Professor Lavelle has mentioned that 1x10^-3 is okay too, just as long as it doesn't change the value next to it (which in your example of .032, a value of x around 1x10^-3 may actually have some effect).

Aydin Karatas 1F
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### Re: when to assume x is insignificant

Another test to see if the approximation is acceptable is to check (after approximation) x < 5% of the initial concentration where x = the final concentration (so taking the ionization/protonation %).

Samir 3I
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### Re: when to assume x is insignificant

Yes I believe we can assume x is insignificant when the concentration is less than 1.0x10^-3. Another way to be sure is that if you use the assumption and calculate for x and the final x is less than 5% of the initial concentration then you assumed correctly.

Christine Ma 3L
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### Re: when to assume x is insignificant

If the calculated x (when omitted) is less than 5% of the initial concentration, then the approximation (that omits x) is valid. If it's greater than 5% then x is not negligible and can't be ignored, which means you have to go back and use the quadratic formula to solve for x.

Natalie 3k
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### Re: when to assume x is insignificant

Hi, I was confused about this too, but I remember Dr. Lavelle saying that if the equilibrium constant is under 1x10^-3 then you can assume that the change is insignificant, but I've read that 1x10^-4 is more accurate. It can be assumed to be insignificant if it is less than this and doesn't change the value gotten during calculations, which is how I check if it can be done or not.

Mariah Disc 2C
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### Re: when to assume x is insignificant

You can assume x is insignificant when the concentration is less than 1.0x10^-3! This can also be done by using the assumption and calculating for x and if the final x is less than 5% of the initial concentration then you assumed correct.

Hasan Mirza 3F
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### Re: when to assume x is insignificant

In some of the sapling problems, the difference between the Ka and concentration needs to be more than 1000 which is 10^3 but in some cases it is better to use 10^-4.

Rose_Malki_3G
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### Re: when to assume x is insignificant

When the k value is less than 10^-4 we can assume the x value is insignificant. Also if the percent ionization is less than 5%, we know the x value is insignificant.

305572629
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### Re: when to assume x is insignificant

Assume that x is irrelevant in an ICE table when the equilibrium constant is less than 10^-4

Zihan Liu 2K
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### Re: when to assume x is insignificant

I think you would assume x is insignificant is when K is smaller than 10^(-4)
To confirm that x is indeed small, use x divided by the initial concentration of the acid/base. If the results are smaller than 5%, then x is indeed insignificant.

I'm not too sure whether this could be applied to bases as well because in base calculations, we normally would let x represent the concentration of OH-. Since it's a base, x is deemed to be very small. Therefore, either this rule can be applied to all the bases, or you simply cannot use it with bases.

Izamary Marquez 2H
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### Re: when to assume x is insignificant

In addition is there a certain way we should approach every problem whether it is negligible or not? Should we always solve for it anyway?

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### Re: when to assume x is insignificant

I think it would be best to always check using the ionization percentage.

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### Re: when to assume x is insignificant

We can assume the x value is insignificant if the equilibrium constant is less than 10^-3 (safer if less than 10^-4 as Dr. Lavelle mentioned in lecture) and if the ionization percentage is below 5%.

Jordan Tatang 3L
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### Re: when to assume x is insignificant

when the equilibrium constant is less than 1.0 x 10^-4. you can verify if the approximation is valid by finding the percent ionized and if it is less than 5% than the approximation is valid.

Gicelle Rubin 1E
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### Re: when to assume x is insignificant

Natalie 3k wrote:Hi, I was confused about this too, but I remember Dr. Lavelle saying that if the equilibrium constant is under 1x10^-3 then you can assume that the change is insignificant, but I've read that 1x10^-4 is more accurate. It can be assumed to be insignificant if it is less than this and doesn't change the value gotten during calculations, which is how I check if it can be done or not.

Thanks for your clarification! :)

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### Re: when to assume x is insignificant

I remember Dr. Lavelle mentioning that a k value of 10^-4 or less is safe enough to assume that x is insignificant. Also, if the percent ionization of a reaction is less than 5% you can also assume x is insignificant.

Nicoli Peiris 1B
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### Re: when to assume x is insignificant

I believe he said to use the 5% ionization percentage rule! Where if your % is less than 5%, the approximation is valid.

Cora Chun 2D
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### Re: when to assume x is insignificant

You can approximate when the constant is less than 10^-4, but make sure to always double check if your x value is less than 5% of the initial concentration (x/initial conc.*100<5). If it is greater than 5%, you need to use the quadratic formula.

Eileen Quach Dis 2A
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### Re: when to assume x is insignificant

When the equilibrium constant is less than 10^-4 you can assume x is insignificant and not include it in the denominator. If you really want, you can verify if it was okay to use the approximation for a given problem by checking if the percent ionization is less than 5%.

Coleman Morrow
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### Re: when to assume x is insignificant

I was under the assumption that x is insiginificant when it is greater than 1000x smaller than the molarity. So if x is 1.2E-7, and your molarity is 0.042 it would be insignificant.

Mary Shih 3J
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### Re: when to assume x is insignificant

I have 10^-4 in my notes so I would go with that value instead of -3

VincentLe_3A
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### Re: when to assume x is insignificant

According to the lectures, it is safe to approximate when the equilibrium constant K is less than 10^-4. To be sure that approximation is appropriate, always check for the 5% rule afterwards, where if the percent ionization is less than 5%, then approximation is appropriate.

Daniel Huynh 2J
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### Re: when to assume x is insignificant

X is insignificant in equilibrium calculations when x is extremely small or less than 5% of the value it is changing.

Lorraine Medina 3E
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### Re: when to assume x is insignificant

Dr. Lavelle said x is assumed insignificant when it is less than 10^-4. Hope this helps!

jessicasilverstein1F
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### Re: when to assume x is insignificant

I would assume this when x is lower than 10^-4

Lucy_Balish_3G
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### Re: when to assume x is insignificant

We can assume x is insignificant when the equilibrium constant is less that 10^-4.

Katie Le 3K
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### Re: when to assume x is insignificant

When Ka value is 10^-5. If you are unsure, always double check using percent ionization. If its above 5% you cant use the shortcut

ellenulitsky Dis 1I
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### Re: when to assume x is insignificant

Use the 5% rule which is the same way of doing percent ionization! Hope this helps!

Rylee Mangan 1K
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### Re: when to assume x is insignificant

In lecture it was mentioned we can approximate when Ka < 10^-4 but I like to always use the 5% rule to be safe!

Chloe Shamtob 2H
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### Re: when to assume x is insignificant

You would make x negligible for equilibrium problems if the Ka or Kb is 10^-4 or smaller. Therefore, the change X would be too small to be significant. Make sure that the shortcut is allowed by finding the % ionization. If the percent ionization is less than 5%, your approximation is valid.

Alen Huang 2G
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### Re: when to assume x is insignificant

You can assume x is insignificant if the ka or kb value is below 10^-4, but make sure you use the 5% rule to make sure!

Brenda Silva 1B
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### Re: when to assume x is insignificant

We can assume that x is insignificant when Ka or Kb are below 10^-4, to make sure your answer is correct use the 5% rule.

reyvalui_3g
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### Re: when to assume x is insignificant

It is always good to use the 5% rule to determine if x is insignificant.

Ryan Agcaoili 2E
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### Re: when to assume x is insignificant

If the value is smaller than 10^-4, then you can utilize approximation.

Andy Hon 3E
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### Re: when to assume x is insignificant

You can approximate x, when its Ka or Kb value is less than 10^-4.

Kylie Joe 2A
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### Re: when to assume x is insignificant

I believe when you approximate x and it is smaller than 1x10^-5, you can keep the approximation and assume that the -x is insignificant

Sejal Parsi 3K
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### Re: when to assume x is insignificant

I think that if the equilibrium constant is under 1x10^-3, you can assume that the change is insignificant, but I've seen that 1x10^-4 is more accurate. It can be assumed to be insignificant if it doesn't change the value you get after calculations.

Kathy_Li_1H
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### Re: when to assume x is insignificant

Hi! You can assume x is insignificant when the initial concentration is 1000 times larger than the Ka or Kb. If you aren't sure, the safest bet is to not assume x is insignificant.

Nina Fukui 2J
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### Re: when to assume x is insignificant

I use 10^-4

Rahul Sobti 1E
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### Re: when to assume x is insignificant

10^-4 and you can always check if the percent ionization is less than 5 % by H+/HA or OH-/AOH

Navdha Sharma 3J
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### Re: when to assume x is insignificant

I remember that Dr. Lavelle said in his lectures that whenever K is less than 10^-4. Also, you can always check it. If the value of x is less than 5% of the initial molarity, you are good to go!

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### Re: when to assume x is insignificant

When the equilibrium constant is 10^-4 or smaller, it's safe to just approximate. However, you can run into errors when you're calculating percent ionization. If your percent is greater than 5%, then you're going to have to re-do the calculation without the approximation.

Sophia Wendin 3L
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### Re: when to assume x is insignificant

I think the general rule is 10^-4 but it's good to check and make sure x is less than 5% of the initial value.

Justin Lin 1B
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### Re: when to assume x is insignificant

I would assume X to be insignificant when the K value is 10^-5. You can double check that your approximating correctly by using the 5% rule.

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### Re: when to assume x is insignificant

Also, I believe for weak acids/bases x is insignificant because you know that because they are weak, they will have a K value that is considered small.

Alison Perkins 2B
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### Re: when to assume x is insignificant

When the equilibrium constant is less than 10^-4 in your ICE table, you can assume that x is negligent in K calculations.

Neel Bonthala 2G
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### Re: when to assume x is insignificant

When working with acid and base equations, use the Ka or Kb value to determine if x is insignificant. If the equilibrium constant is less than 10^-4, it's probably safe to assume that not much of the initial amount of the acid/base was deprotonated/protonated. However, to be even more careful, there's one more step you should take. If the equilibrium constant is small enough and you assume x is insignificant, make sure to divide the final equilibrium concentration of H+/OH- and divide it by the initial concentration of the acid/base used. If the percent is less than 5% you're fine. If the percent is greater, then you probably cannot assume x is insignificant, and you should solve it again.

Chinmayi Mutyala 3H
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### Re: when to assume x is insignificant

Less than 10^-3 but Lavelle said when k is less than 10^-4 to be safe; also if you divide x by the initial concentration and get less than 5%, you know that your assumption is ok.

Taylor Newville 1C
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### Re: when to assume x is insignificant

K is considered small when it is less than 10^-3, but Dr. Lavelle said that K should be less than 10^-4 to use successive approximation. Always check that the percent ionization is less than 5% to know that x is insignificant because there are many exceptions to the rule.

Siwa Hwang 3G
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### Re: when to assume x is insignificant

You can assume that x is insignificant when K is less than 1x10^-4 !!

Ashley Kim 3H
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### Re: when to assume x is insignificant

If in the expression (x)/(initial concentration) x 100 is less than 5%, you can ignore the x value!

Keon Amirazodi 3H
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### Re: when to assume x is insignificant

When the concentration is less than 10^-3, x can be assumed to be insignificant.

Emma Strassner 1J
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### Re: when to assume x is insignificant

If K it is less than 10^-3 you can assume, but to be safe it is better to approximate if K is less than 10^-4.

Claudia_Danysh_2B
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### Re: when to assume x is insignificant

We can assume that x is insignificant whenever K is less than 10^3!!

Liam Bertrand 3
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### Re: when to assume x is insignificant

You can only assume x is insignificant if the Ka/Kb value is 1x10^-3 times smaller. Basically when Ka or Kb is really really small you can disregard the x

Karen Elrayes 1L
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### Re: when to assume x is insignificant

It's usually when k is less than 10^-3 but you have to check the percent ionization by diving x by the initial concentration and see if it is less than 5%. Usually when k is super small, it is very likely you can approximate.

Shivani Kapur 2J
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### Re: when to assume x is insignificant

Dr. Lavelle said to check and see if the ionization percentages are less than 5% but also if the K is less than 10^-3, then you can approximate.

manisha_joseph_1H
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### Re: when to assume x is insignificant

We can assume that x is insignificant in the case of 0.32 - x for instance when the Ka, Kb, or K given is less than 1.0 x 10^-4 and the percent ionization or deprotonation is less than 5%.

Brianna Chen 3F
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### Re: when to assume x is insignificant

The rule of thumb I like to use is if the K value is less than 10<-3 (meaning the values are typically 10^-4), we can assume that the approximation rule will be okay to use. However, for acids and bases, I like to check the percentage ionization/protonation to see if it holds to the 5% rule.

Simran Bains 2C
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### Re: when to assume x is insignificant

when k is equal to or smaller than 1.0x10^-5

Caelin Brenninkmeijer 1G
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### Re: when to assume x is insignificant

It's usually safe to use this approximation when K is equal to or greater than 10^-4.

Sarah Huh 1K
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### Re: when to assume x is insignificant

You can assume x is insignificant if it is below 1.0E-4.

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### Re: when to assume x is insignificant

You can assume that x is insignificant if the value that you receive for percent ionization is less than 5%. This would mean that your original substance barely dissociated, so the number that you would be subtracting from the initial is negligible.

Presley Gao 2C
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### Re: when to assume x is insignificant

It is fine or restricted to assume x is so insignificant we can keep it out when it is less than 5% of the initial concentration.

305405193
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### Re: when to assume x is insignificant

x is insignificant when you get a percent ionization less than 5% and when k is less than 1.0 x 10^-4

Tobie Jessup 2E
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### Re: when to assume x is insignificant

you cn say x is insignificant when solving the quadratic if the k value is 10^-4 or less.

joshtully
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### Re: when to assume x is insignificant

It is insignificant when it is by 10^-4 or less.

Luveia Pangilinan 1A
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### Re: when to assume x is insignificant

in the lecture, Dr.Lavelle prefers to determines if its insignificant if its lets than 10^-4 rather than 10^-3.

Queena Chu 3E
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### Re: when to assume x is insignificant

We can assume that x is insignificant when the concentration is less than 1.0x^-3. A more accurate way is to see if you can assume that is to solve for x and the assumption is valid of final x is less than 5%.

DPatel_2L
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### Re: when to assume x is insignificant

We can assume it is insignificant when x is less than 10^-4.

Aanya Tanti 3C
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### Re: when to assume x is insignificant

You only use it when the equilibrium constant is less than 1.0x10^-4. To check after making the assumption, make sure that x/equilibrium constant is less than 5%

RyanKopeikin_2I
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### Re: when to assume x is insignificant

I would say if K<10^-3 then you can assume X is insignificant, and if K<10^-4 then you can DEFINITELY assume X is insignificant.

Akriti Ratti 1H
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### Re: when to assume x is insignificant

X is insignificant when K<10^-4

Kimiya Aframian IB
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### Re: when to assume x is insignificant

Cristian Cortes 1L wrote:For some questions on sampling week 2, where we would have a number like .032-x and equal it to Kb for an example, when is it fine or restricted to assume x is so insignifcant we can keep it out?

Hi! A general rule for knowing when assuming x is insignificant is okay is if the k value is less than 10^-4. To be sure, you can also calculate the percent dissociation, and if it 5% or less, it is okay to assume x is insignificant. Hope this helps!

Hasan Mirza 3F
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### Re: when to assume x is insignificant

The general rule is 10^-4 or smaller is fair game. But sometimes you need to make sure that the percent produced is less than 5%.

gabbi_r2C
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### Re: when to assume x is insignificant

generally speaking, if the equilibrium constant is below 10^-3 or above 10^3, you can assume x is insignificant. to be safe, you can use 10^-4 and 10^4 instead.

Jeremy Wei 2C
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### Re: when to assume x is insignificant

I believe that Lavelle said during lecture that if the equilibrium constant is below 10^-4 (to be on the safe side), you can assume x as insignificant.

Jonathan Malau 1F
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### Re: when to assume x is insignificant

It can be assumed that x is insignificant when concentration is less than 1.0x10^-3. Additionally, if the assumption is used, the final x should be less than 5% of the initial concentration.

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### Re: when to assume x is insignificant

He said different things in different lectures, but I think his latest verdict was 1x10^-4 (smaller the better basically). It'll probably be obvious when he wants to omit it though, so I wouldn't worry too much.

Carly_Lipschitz_3H
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### Re: when to assume x is insignificant

We can assume X is insignificant if the Ka or Kb value is less than 10^-4. To be sure, you have to do the 5% rule as well.

Gian Boco 2G
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### Re: when to assume x is insignificant

When K is below 10^-4

Diana Aguilar 3H
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### Re: when to assume x is insignificant

Hi! I believe we can assume x is insignificant when the k value is less than 10^-4

Ephrem Gerald 2A
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### Re: when to assume x is insignificant

Whenever the K value is less than 10^-4, professor said it is okay to assume that x is insignificant. He also mentioned a check where you could choose x to be significant and one where it isn't and compare the answers and if there is lower than a 5% error, than it was okay to assume x is insignificant.

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