According to my notes, 100 can either have 1 or 3 significant figures. It says the way to determine which it is, is by other factors. That's why I want to know what it means by "100 is exact"
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3 significant figures not 1. A '0' is only significant AFTER a number Higher. 100 to be exact means there is no decimal places. It's exactly 100. Not 100.1 or 99.9. 100