A shoe shop noted the sizes of the last 12 pairs it sold: 7, 8, 6, 8, 9, 7, 8, 10, 8, 7, 6, 9. Which size is the mode?

Counts: size 6 – 2, size 7 – 3, size 8 – 4, size 9 – 2, size 10 – 1. Size 8 occurs most often, so the mode is 8. (4 is its frequency, not the size.)