Significant Figure Help?

Question

give the number of significant figures
1. the number of eggs (12) that make up a dozen
2. 2.000 x 10^2 m
3. 40,500 cm

Answer 1

The person above me made a mistake... 1 and two are correct.
1->2
2->4
3-> 3 Only 3 significant digits, trailing 0's before the decimal are not significant. so only the 405 are significant, the remaining two digits are not. If you wanted to show the same value, but with all significant digits, you would write 4.0500 x 10^4

Answer 2

The answer is what it states: the number of digits which are significant. But this isn't always obvious. 12 eggs is 2 significant figures (exactly 12, not 12.1). The next requires definition. 2.000 has four significant figures if it is exactly 2.000 and not between 2.1 and 1.9. If so it should be 2.0 x 10^2. #3 requires judgement. Exactly 40,500 would be 5 significant figures but probably is 3 significant figures meaning 40.5x10^2. But that is awkward so 40,500 uses the last two zeros to place the decimal point. But it could mean exactly 40,500; you need to check the context of its use.

Answer 3

1. 2
2. 4
3. 5