Ok, so I have to give the answer in the correct amount of significant digits.

The diameter of a circle is 16.0m. Find the area.

I know how to work the answer out correctly, but I am unsure of how many significant digits I should use..

16.0m/2=8

pi(8^2) = area

so... do I use 3 significant digits (based on 16.0) or do I use 1 significant digit (based on 8)?