General Rules of Sig Figs with Example Questions

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Gabriel Ordonez 2K
Posts: 113
Joined: Sat Jul 20, 2019 12:15 am

General Rules of Sig Figs with Example Questions

Postby Gabriel Ordonez 2K » Thu Oct 03, 2019 10:54 am

What are the general rules when applying significant figures to various types of number values? In essence, if we see specific numbers, how do we know what type of rule applies and how to apply it?

For example, how many significant figures do the following have:
0.0007890 = ?
010056.0 = ?
14 = ?
28. = ?
10.0005609 = ?
0 = ?
00349.09000 = ?

Your assistance would help me clear a few misconceptions I have about significant figures. Thank you!

Audrie Chan-3B
Posts: 50
Joined: Thu Jul 25, 2019 12:17 am

Re: General Rules of Sig Figs with Example Questions

Postby Audrie Chan-3B » Thu Oct 03, 2019 11:30 am

To find the significant figures of a number, you look for non-zero numbers or trapped zeros. Trapped zeros would include zeros that are between two non-zero numbers. For example, the sig fig of 14 would be 2. If the number has a decimal point, then you look for the first non-zero number and count after it (the zeros afterwards would count). So, the sig fig for 0.0007890 would be 4 and the sig fig for 010056.0 would be 6 (the zero after the decimal point counts). Trailing zeros are insignificant, so the zeros in 400 would not count (400 has a sig fig of 1), but if you put a decimal after 400 (400.) then the sig fig would be 3 (trailing zeros in a decimal are significant). 0 itself is one significant figure, and if you were to find the sig fig of 0.00, then it would have 3.

0.0007890 = 4
010056.0 = 6
14 = 2
28. = 2
10.0005609 = 9
0 = 1
00349.09000 = 8

I hope this helps; sorry if it's a bit confusing.

cassidysong 1K
Posts: 100
Joined: Fri Aug 30, 2019 12:15 am

Re: General Rules of Sig Figs with Example Questions

Postby cassidysong 1K » Thu Oct 03, 2019 12:42 pm

The general rule for the number of sig figs for an answer is exactly like what the previous reply said; they are based on the amount of numbers that aren't zero or any zeros that are in between other numbers. For example, 25.7 has three sig figs where as 25.07 has four sig figs. Another rule is that the amount of zeroes after a decimal only count if they follow a number that isn't zero so for 0.0007890, the number of significant figures is 4. The preceding zeroes don't contribute to the number of sig figs.
Like the previous reply said:
010056.0 = 6
14 = 2
28. = 2
10.0005609 = 9
0 = 1
00349.09000 = 8

Emily Vainberg 1D
Posts: 102
Joined: Sat Jul 20, 2019 12:15 am

Re: General Rules of Sig Figs with Example Questions

Postby Emily Vainberg 1D » Thu Oct 03, 2019 1:42 pm

Here are some tips when counting significant figures
- pay attention to where the decimals are placed
ex: 1000. vs. 1000
- Since there is a decimal at the end for the first number it has 4 significant figures where as the second number only has 1 significant figure
- think about what numbers would stay if it was rearranged exponentially using 10^x

Here are the answers for the ones you asked:
0.0007890 = 4 sig fig
010056.0 = 6 sig fig
14 = 2 sig fig
28. = 2 sig fig
10.0005609 = 9 sig fig
0 = 1 sig fig
00349.09000 = 8 sig fig

Manav Govil 1B
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Re: General Rules of Sig Figs with Example Questions

Postby Manav Govil 1B » Thu Oct 03, 2019 1:58 pm

What tricks me up the most is the zeroes involved in sig-figs. I'll show you why:

250000 has 2 sig-figs
250000. has 6-sig-figs
250.000 has 6 sig-figs
250.001 has 6 sig-figs
1.00025 has 6 sig-figs
0.00025 has 2 sig-figs

You have to memorize what effects sig-figs so that you know how many sig-figs there are in a number, and utilize that data to correctly answer the question after a calculation. It can be tricky at times, but important nonetheless when involved in a lab-setting.

This is also where accuracy comes in. Think about it. Let's say that the correct answer is 25.325 g. After calculations, you compute the number 25.325342 g. But part of your calculation had a number that was only two sig-figs. Therefore, your final calculated value is actually 25. g. That makes your data less accurate than someone who had a low sig-fig of three in their calculations (25.3 g). Sig-figs are really important in the scientific world.

I hope this helps.

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