Question

A waiter received a 20% tip of $5 p, how much was the original bill?

Answer 1

well, the assumption is that the tip is exempt from the bill, so the 20% is really 20% of the whole bill and not part of it.

well, the amount was really "x", which oddly enough is the 100%, and we know that 20% of that is 5 bucks.

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} x & 100\\ 5& 20 \end{array} \implies \cfrac{x}{5}~~=~~\cfrac{100}{20} \implies \cfrac{x}{5} ~~=~~ 5\implies x=25`