You use 3 significant digits, because that's the data you were given. More formally the calculation is:
16.0m/2 = 8.00m
pi(8.00m)^2 = area
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..
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)?