Math & Logic · Ages 7–9
Riddle #70
The big clock in the town square bongs once for every hour — 4 bongs at 4 o'clock, 7 bongs at 7 o'clock. It takes the clock 6 seconds to bong 4 o'clock. How long does it take to bong 7 o'clock?
You solved this one before
Answer: 12 seconds
The seconds are in the gaps between the bongs, not in the bongs. Four bongs have only three gaps between them, so each gap is 6 ÷ 3 = 2 seconds. Seven bongs have six gaps: 6 × 2 = 12 seconds. (The tempting answer is 10 and a half — but that would mean a gap after the last bong, and there isn't one.)