Question

John spends 30% of his income on food and 40% of his income on rent each month. His rent is $1,800. How much did he spend on food

Answer 1

`\bf \begin{array}c\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{30\% of 1800}}{\left( \cfrac{30}{100} \right)1800}\implies 540`