There are a few numbers listed and the goal is to figure out how many significant figures are in each number. I’ll discuss which of the significant figure rules I’m using, but otherwise they can be found on page 21.
A: 556 Km : This has three significant figures (Rule 1 states all nonzero digits are significant)
B: 7 pennies : One significant figure. I’m not entirely sure on this one and I think it might be considered an exact number which means it has no uncertainty. In that case, it could be written as 7.000000 pennies, which means there is an unlimited amount of significant figures. When I first looked at this one I was thinking that if it was being measured in value instead of quantity (i.e. 0.07) that the answer might be different, but that would also be just 1 significant figure. Again, I’m not 100% certain on this one.
C: 1.01 x 10^5 m : 3 significant figures. (Rule 1, Rule 2 states all interior zeros are significant, Rule 4c states trailing zeros before an implied decimal point are ambiguous)
D: 0.00099 s : 2 significant figures (Rule 1, and Rule 3 states leading zeros are not significant)
E: 1.4500 Km : 5 significant figures (Rule 1, and Rule 4a states trailing zeros after a decimal point are always significant)
F: 21,000 m : Ambiguous (again, Rule 1 states all nonzeros are significant, but Rule 4c states trailing zeros are before an implied decimal point and are ambiguous)