How do I do calculations with sig figs?

Chemistry
Tutor: None Selected Time limit: 1 Day

So my professor said to shorten your answers down to the smallest number of sig figs in the equation. So for 5.19+1.9+0.842=7.932, you would make it 7.9 because of the "1.9" in the equation. So why for 8.41+1.33x2.8=12.134, would you make it 12.1? Shouldn't it just be 12? PLEASE HELP NOTHING ONLINE IS HELPING!!!!!!

Aug 31st, 2015

Hi there! Thank you for the opportunity to help you with your question!

Very good question! Sig figs can be very confusing! Whenever we are multiplying or dividing numbers, it is true that we only keep as many significant figures as the least number, so when we evaluate 1.33 * 2.8 we get 3.7 (after rounding).

Now we are left with

8.41 + 3.7

The rule for addition is slightly different: "For results obtained using addition or subtraction, the number of places after the decimal point in the result should be less than or equal to the number of decimal places in every term in the sum."

That is, sig figs determine how many decimal points  will there be in the answer. Since our worst measurement is the "3.7", we know the final answer will have one decimal point.

After doing the addition, we get 12.1, with one decimal point.


Please let me know if you need any clarification. Always glad to help!
Aug 31st, 2015

Can you also help me make sense of this problem? (25.36-4.15)/2.317. It tells me the answer is 9.154 but I can not figure out why.

Aug 31st, 2015

Unfortunately due to website policy, I am not allowed to answer a new question here, only clarify my previous answer. If you can make a new post, I would gladly explain it. Hope you understand.

Aug 31st, 2015

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