Question

A copy machine makes 189 copies in 5 minutes and 15 seconds how many copies does it make per minute 

Answer 1

keeping in mind that a minute has 60 seconds, so 5 minutes is really just 300 seconds, so 5 mins and 15 seconds is 315 seconds.

now let's reword it.

if the machine makes 189 copies in 315 seconds, how many does it make in 60 seconds?

`\begin{array}{ccll} copies&seconds\\ \cline{1-2} 189 & 315\\ x& 60 \end{array} \implies \cfrac{189}{x}~~=~~\cfrac{315}{60} \\\\\\ \cfrac{ 189 }{ x } ~~=~~ \cfrac{ 21 }{ 4 }\implies 756=21x\implies \cfrac{756}{21}=x\implies 36=x`