In a training batch of 60 people, 45 hold a driving licence and 38 have completed the first-aid course. Which of the following must be true?

The two groups together account for 45 + 38 = 83 memberships spread over only 60 people, so at least 83 - 60 = 23 people must fall in both. The overlap could be larger - up to 38 - so 'exactly 23' is not forced. And with an overlap of 23 the three groups account for 22 + 23 + 15 = 60 people, leaving nobody outside, so the second option can fail; the third can fail whenever a first-aid holder has no licence.