Problem #WSP-000549

Problems Combinatorics
 11–15  2.0

Problem

A book club with 37 members is reading the following books: “Brave New World", “Dracula" and “Flatland". Each member chose one of the books, though some people chose more than one book. We know that:

  1. 23 people chose “Brave New World";

  2. 18 people chose “Dracula";

  3. 26 people chose “Flatland";

  4. 7 people chose all three books.

How many people chose at least two books?