Significant digits correct?

Question

For 24.15 - 20.32, would you need to round to 4 significant digits, since it becomes a number less than 10?

I know that when you subtract up and down, when no column has both non-significant digits, then you just make it 3.83? No need for four significant figures?

Samem for 22.55 - 20.33? would be just 2.22, and if it was 20.13 - 20.13, it would just be 0.00?

Significant digits are kind of confusing I guess..

Also, for 0.09/ 3.66 x 100%, would this be rounded to something like 2 percent? just 1 significant digit? and why?

Answer 1

"For 24.15..." The answer is no. Keep four sig figs. You started out with them. They are justified now.

"Same for..." Same answer.

"Also..." Two sig figs., because 0.09 is known to two sig figs.

Answer 2

For addition and subtraction you don't really count significant figures, you count places to the right of the decimal point. So the answer to 24.15 - 20.32 is 3.83. The answer could have any number of significant figures as long as it doesn't have more than two places past the decimal point since that is the fewest places past the decimal point in the problem (in the numbers 24.15 and 20.32).

For 0.09/3.66 x 100%, you answer can have only 1 significant figure because of the number 0.09 (it has only 1 sig.fig). Your answer can only have as many sig figs as the FEWEST in the problem. The number 100 (which technically only has 1 sig fig) really shouldn't be considered because it is not a measurement, it is an "exact" number. You should assume the number is exactly 100 with an infinite number of zeros after the decimal point. Significant figures really only apply to numbers that represent measurements.