Question

I'm adding these three atomic weights (40.1+12.0+48.0) together, and I got 100.1
How can I round my answer to three significant figures? thank you!

Answer 1

you by adding now have four significant figures. When adding, you keep all place values that were significant.

if it had been
34 + 12.2+6.0=52. Cant do the tenths, as tenths was not significant in the first numeral.

Answer 2

To add a little clarification to the answer already posted.
The correct answer to 3 s.f. is 100. and the period at the end is necessary and it not the end of the sentence. That sometimes leads to confusion and another way to do it to write 1.00E2 and that way a period is not necessary. If you leave it as 100 and don't put a period you only have 1 s.f.