Question

During a certain day, a worker did 77 parts. He usually does 55 parts per day. What was the percent by which he increased the usual number of parts?

Answer 1

So, he usually does 55 only, but this one day he did 77, 77 - 55 is 22, so he did 22 more this one day.

if we take 55 to be the 100%, what is 22 off of it in percentage anyway?

$\bf \begin{array}{ccll} amount&\%\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 55&100\\ 22&p \end{array}\implies \cfrac{55}{22}=\cfrac{100}{p}\implies p=\cfrac{22\cdot 100}{55}$