### Decimal point

Posted:

**Wed Oct 03, 2018 11:55 pm**Can someone explain the difference in sig figs between 125 and 125. , if there is one?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=9&t=32970

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Posted: **Wed Oct 03, 2018 11:55 pm**

Can someone explain the difference in sig figs between 125 and 125. , if there is one?

Posted: **Wed Oct 03, 2018 11:57 pm**

Both of the values have the same number of significant figures: 3 sig figs. Adding a decimal point is tricky when it comes to sig figs!

Posted: **Thu Oct 04, 2018 12:00 am**

If it had been 120 instead of 125, for example, 120 is only two significant figures while 120. is three. It has to do with zeroes at the end of numbers

Posted: **Thu Oct 04, 2018 12:32 am**

125 and 125. have the same number of sig figs! Sometimes it may be confusing if the numbers end in 0. For example 120 and 120.0 have different sig figs because of the decimal in place.

Posted: **Thu Oct 04, 2018 1:04 am**

These both have the same amount of significant figures. During one of the lectures, Dr. Lavelle had stated that significant figures are easily understandable when you put them into scientific notation. For example, these two numbers(125 and 125.) are both 1.25 * 10^2 and have 3 significant figures.

Posted: **Thu Oct 04, 2018 3:02 pm**

Can someone explain what the rule is for 120 to be only two significant figures while 120. is three

Posted: **Thu Oct 04, 2018 3:15 pm**

Basically, zeroes before the decimal point with the decimal point behind them and zeroes following the decimal point are significant. The only zeroes that aren't significant are zeroes in a number like 120 where they are no decimal points.

Posted: **Thu Oct 04, 2018 3:18 pm**

Does that mean 120. has 3 sig figs and 120 has two sig figs?

Posted: **Thu Oct 04, 2018 8:27 pm**

Yukta Italia 3I wrote:Does that mean 120. has 3 sig figs and 120 has two sig figs?

Yes!

Posted: **Thu Oct 04, 2018 8:38 pm**

For these types of values involving leading zeros behind a decimal, (e.g., .041), would you disregard the 0 as a significant figure?

Posted: **Thu Oct 04, 2018 9:26 pm**

Bianca Barcelo 1G wrote:For these types of values involving leading zeros behind a decimal, (e.g., .041), would you disregard the 0 as a significant figure?

I believe for the example of 0.041 there would be 2 sig figs so the 0 is not a sig fig

Posted: **Thu Oct 04, 2018 10:01 pm**

If students are still struggling with significant figures, please refer to this accessible document summarizing significant figure rules: https://lavelle.chem.ucla.edu/wp-conten ... OUT_SF.pdf

Posted: **Sun Oct 07, 2018 5:42 pm**

The reason 120 has 2 significant figures while 120. has 3 is that the decimal tells you that any zeros before and after it are considered significant. So, 120 has 2 sig figs, while 120. has 3 sig figs and 120.0 has 4 sig figs. The zeros after nonzero numbers are only significant if there is a decimal. 1200 only has 2 sifg figs because the zeros are not followed by a decimal.

Posted: **Sun Oct 07, 2018 5:47 pm**

120. definitely has 3 significant figures. 120 (without the decimal point) however is ambiguous and therefore it is better to use scientific notation: 1.20 x 10^2 (this would definitely have 3 significant figures).

Posted: **Sun Oct 07, 2018 6:14 pm**

Manya Kidambi 3I wrote:Can someone explain the difference in sig figs between 125 and 125. , if there is one?

125 and 125. both have 3 significant figures. However, 125.0 has 4 significant figures. The reason being that there is a 0 behind the decimal point in 125.0 while 125. does not have a 0. 125.00 would have 5 sig figs, 125.000 would have 6, and so on.