In a survey among 40 people, 25 read guardian and 19 read tribune. If nobody read either of the paper, how many read both paper?
"|A \\cap B| = |A| + |B| - |A \\cup B|"
since we have in union 40 people, A is a set of 25 guardian readers and B is a set of 19 tribune readers, we get that both readers
"|A \\cap B|" = 25 + 19 - 40 = 4
Answer: 4 people read both paper
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