Two dice are thrown. On each die the numbers on opposite faces add up to 7. The two faces resting on the table add up to 9. What do the two top faces add up to?

On each die the top and bottom together make 7, so for the two dice the four faces together make 14. Taking away the two bottom faces leaves 14 − 9 = 5 on the two tops. The traps: 9 assumes the tops copy the bottoms, 7 uses just one die's pair, and 3 comes from subtracting 9 from 12 instead of 14.