Question

what is the sum of 2.7 grams and 2.47 grams expressed in the correct significant digits?

Answer 1

5.2

Answer 2

There are only two sig figs because when adding with significant figures, you add to the decimal point on the farthest left.

Answer 3

Here's a link that is a bit more scientific in explaining it than I am. :) Good luck!
http://chemistry.bd.psu.edu/jircitano/sigfigs.html