A bookshelf holds 45 books of two different thicknesses. Thin books are 1 inch wide and thick books are 2 inches wide. If the total width of the bookshelf is filled and there are twice as many thin books as thick books, how many thin books are there?
30
Let t be the number of thick books. Then there are 2t thin books. Total books = t + 2t = 3t = 45, so t = 15 thick books. That means there are 2 x 15 = 30 thin books.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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