Question

A restaurant customer left $1.05 as a tip. The tax was 8% and the tip was 15% of the cost including tax.

a. Which information is not needed to compute the bill after tax and tip?
b. What was the total bill?

Answer 1

well, the bill was actually "x", which oddly enough is the 100%, but we also know that the tip was $1.05 and that's 15% of the whole bill plus tax.

so if we know that 1.05 is 15% of "x", what the dickens is "x"?

`\begin{array}{ccll} amount&\%\\ \cline{1-2} 1.05 & 15\\ x& 100 \end{array} \implies \cfrac{1.05}{x}~~=~~\cfrac{15}{100} \\\\\\ 105=15x\implies \cfrac{105}{15}=x\implies 7=x`

well, as you can see, we know the tax was 8%, but, it doesn't really matter if it had been 25% or who knows, so long we know that 1.05 is 15% of the whole smack.