A public library opens Monday to Friday only, and is also shut on the holiday shaded orange. On how many days is it open in the month shown?

This June starts on a Friday and has 30 days. Weekends: Saturdays 2, 9, 16, 23, 30 and Sundays 3, 10, 17, 24: 9 days, leaving 21 weekdays. The orange holiday, 5 June, is a Tuesday, so open days = 21 − 1 = 20. (21 ignores the holiday.)