Question

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?

Answer 1

$|A \cap B| = |A| + |B| - |A \cup B|$

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