Answer
$1 \times 10^{-5} \%$ ; 8 significant figures.
Work Step by Step
Percentage uncertainty = $\frac{2 m}{20000000 m} \times 100 \%=1 \times 10^{-5} \%$.
If a distance of 20,000,000 m changes to 20,000,002 m, the GPS has to be able to tell the difference. Distances must be measured to 8 significant figures.
