Chime spacing
A clock tower has a bell that rings out every hour of the day--for example, 3 chimes at 3 PM, etc. These hourly tolls are spaced 1.5 seconds apart. The clock also chimes once at each half hour.
What is the overall average number of minutes between chimes?
Consider the lengths of the tolls themselves to be instantaneous.
The answer is 8.
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The 1 . 5 seconds is a red herring. Every 1 2 hours there are 1 2 ∗ 1 3 / 2 + 1 2 = 9 0 peals in 1 2 ∗ 6 0 = 7 2 0 minutes.
Divide these and you get 8 minutes per chime.