Candle Timers
The Busy Beeswax Candle Company ("Perfect Precision since 1689") sells only one kind of candle: a very remarkable candle that is guaranteed to burn up in exactly one hour. Unfortunately, these high-precision candles don't burn at a steady pace, so it's no use cutting them into parts to measure out shorter spans. However, they do burn from both ends, a trick which you can use to measure out exactly half an hour, even though the two flames might not meet in the middle.
How many candles do you need to measure out 1 hour and 15 minutes exactly?
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1 solution
You can do it with 3 candles:
First, light candle A from both ends and candle B from one end. When candle A has burned up entirely (after 30 minutes), light the other end of B. B will finish burning after exactly another 15 minutes. When that happens, light both ends of candle C simultaneously to time out another 30 minutes. (30 + 30 + 15 = 1 hour and 15 minutes)