A certain month has exactly five Mondays, exactly five Tuesdays and exactly five Wednesdays. On which day of the week does the 25th of that month fall?

Every month contains four complete weeks (28 days) plus a few spare days, and only the spare days give a weekday its fifth appearance. Three weekdays appear five times, so the month must have 31 days, and the three spare days must be its first three days — Monday, Tuesday, Wednesday. So the 1st is a Monday, and the Mondays fall on 1, 8, 15, 22, 29. Counting on from Monday the 22nd: 23 Tuesday, 24 Wednesday, 25 Thursday. The trap Wednesday comes from stopping at the 24th, and Friday from starting the count at the 22nd itself.