Question

Twelve books cost me $48. What would 13 books cost me?

Answer 1

`$52`

Explanation:

The problem tells you that `12` books cost `$48`, so you can start by figuring out how much would `1` book cost.

To do that, use the given ratio as a conversion factor to go from number of books to cost. You will end up with

`1 color(red)(cancel(color(black)("book"))) * overbrace( ($48)/(12color(red)(cancel(color(black)("books")))))^(color(blue)("given by the problem")) = $4`

You now converted the `$48:"12 books"` ratio to an equivalent `$4:"1 book"` ratio. Use this ratio to find the cost of `13` books

`13 color(red)(cancel(color(black)("books"))) * ($4)/(1color(red)(cancel(color(black)("book")))) = color(darkgreen)(ul(color(black)($52)))`

Notice that you don't have to use the simplified ratio here, you can work directly with the one given to you by the problem

`13 color(red)(cancel(color(black)("books"))) * ($48)/(12color(red)(cancel(color(black)("books")))) = 13/12 * $48 = color(darkgreen)(ul(color(black)($52)))`