Question

A secretary can type 12 pages per hour. There are a total of 152 pages to type. How many pages remain to be typed after 9 hours?

Answer 1

So, she can type 12 pages in 1 hour, how many would she type in 9 hours then?  let's check,

$\bf \begin{array}{ccll} pages&hours\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 12&1\\ p&9 \end{array}\implies \cfrac{12}{p}=\cfrac{1}{9}\implies \cfrac{12\cdot 9}{1}=p$

so in 9 hours, she has that typed that many pages, how many pages remain from the 152?  well 152 - p.