Answer
(a) $2.9 \times 10^8$
(b) $3.8\times 10^{-15} ~m$
Work Step by Step
(a) US population
$290000000 = 2.9 \times 10^8$
(b) diameter of a helium nucleus $0.0000000000000038~m = 3.8\times 10^{-15} ~m$
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