Question

on a 120 question test a student answers 84 correctly what percent of the problem did the student work correctly

Answer 1

well, if we take 120 to be the 100%, what is 84 in percentage off of it?

$\bf \begin{array}{ccll} amount&\%\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 120&100\\ 84&p \end{array}\implies \cfrac{120}{84}=\cfrac{100}{p}\implies p=\cfrac{84\cdot 100}{120}$

Answer 2

That's 84 out of 120 questions answered correctly.  This ratio is

 84
------ * 100% = 70%.
120