About significant numbers, please help.?

Question

In the following, choose the answer with the correct number of significant figures: 4.28 / 81 equals?

A. 0.05284
B. 0.0528
C. 0.053
D. 0.05
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The following description uses accepted SI notation and punctuation: 1 mol = 1 x 1012 nmol, true or false?
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The following description uses accepted SI notation and punctuation: 1 mol = 1 x 109 mmol, true or false?
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And please tell me why if you can.

Answer 1

C
F
F

Multiplication and division result in answers with the same number of significant figures as the number with the smallest number of significan figures in the problem. That's 2 for 81, so the answer has 2. Another example: 4.28/81.0 = .0528.

nano = 10^(-9)
milli = 10^(-3)

Answer 2

C for the first question.