How do you figure out the significant figures in practice problem 7 from Module 12 in Chemistry?


You have to remember that the rules for addition and subtraction are totally different than the rules for multiplication and division (see pp. 25-26). In addition and subtraction, you DO NOT count significant figures. Yes, each of those numbers has two significant figures, but that is not relevant to addition and subtraction.

In addition and subtraction, you look at PRECISION, which is given by decimal place. In each case, the numbers have their last significant figure in the TENS place. (If you convert to decimal, you see this more clearly - 4.8x102 is 480, 8.1x102 is 810). In addition and subtraction, you report your answer to the same precision as the least precise number in the problem. Both of these numbers go to the TENS place, so our answer can go to the TENS place. 1.29x103 does, indeed, go to the tens place (0.01x103 = 10).

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2019-01-29 21:10
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