Spoiler Inside: Solution to Puzzle | SelectShow |
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Let a be the number of sf-romance-only books. Let b be the number of sf-horror-romance books.
The number of romance-only books is then 4 The number of horror-romance-only books is then 2 4 The number of sf-horror-only is There are 1000 books, but 1200 by the three categories. The overlapping eliminates 200. That means that each of the two-category combinations counts twice, and the three-category combination counts three times. The amounts over one account for 200. Therefore Solving the system 7 The solution is 400 sf-only, 250 horror-only, 160 romance-only, 40 sf-romance-only, 90 horror-romance-only, 50 sf-horror-only, and 10 sf-horror-romance. |