Question

It is estimated that there are 10^20 grains of sand on a beach in Florida in April. The beach is heavily eroded by tourists over the peak summer holiday season. Approximately one hundredth of the beach is removed as a result of this erosion. How many grains of sand are removed from the beach?

Answer 1

$\bf \textit{how much is }\frac{1}{100}\quad of \quad 10^{20}?\implies \stackrel{\textit{one hundredth}}{\cfrac{1}{100}}\cdot 10^{20}\implies \cfrac{1}{10^2}\cdot 10^{20} \\\\\\ 10^{-2}\cdot 10^{20}\implies 10^{-2+20}\implies 10^{18} \\\\\\ 1,000,000,000,000,000,000~grains$