Question

Estimate a 15% tip on a dinner bill of $31.22 by first rounding the bill amount to the nearest ten dollars

Answer 1

If you do 31.00×15÷100=4.65 so tip should be 4.65

Answer 2

$\bf \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hspace{5em}\stackrel{\textit{15\% of 31.22}}{\left( \cfrac{15}{100} \right)\stackrel{\textit{rounded up}}{30}}\implies 4.5$