Question

How to write an answer to 3 significant figures

Answer 1

The first three numbers in a overall number. If it's say 15460, you would round to 15500 because it rounds up and trailing 0's don't count unless decimal

Answer 2

It is the first three figures of an answer. However if the answer begins with 0 you don't include that as a significant figure. For example if you have an answer of 0.2034768 to three significant figures it will be 0.203. The first significant figure is always either 1,2,3,4,5,6,7,8,9 and the next two numbers after that.