How many significant figures should I include in my answer?

If the answer is a decimal, you start from the left and ignore any 0s- only count numbers that are not 0. For example, 0.0002 is to 1 significant figure even though there are 3 zeros before the 2. If the answer is a whole number, you start counting from the left and stop when you get to the number of significant figures you need, then round the number you're on depending on what the next number is. For example, 34577 to 3 significant figures is 34600- we have to round the 5 in the 3rd spot because the number after it, 7, is greater than 5, so it should be rounded up.