Chem
posted by Coralie on .
Another confusing significant digit problem. I added 36.6 and 2.4, and divided the result by 4.803. The book says the answer is 7.91, but I don'[t see how that could be, since the lowest number of significant digits in the problem is two (2.4). I think the result should be 7.9, not 7.91. Why is this? Thanks ~Coralie.

Nope. When adding or subtracting, look for the lowest place value that is significant, in this case, tenths.
Numerator is 39.0 three sig digits. 
First, 36.6 + 2.4 gives 39.0, a number with three s.f. When you divide by 4.803 that give you a number of 3 s.f. for the answer; however, the answer isn't 7.91, it is 8.11993 which rounds to 8.12. Did you make a typo in the problem?