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

1 Answer
Stefan V.
Jan 9, 2017

#$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)))#

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