Problem 7 · 2013 Math Kangaroo
Easy
Logic & Word Problems
careful-counting
Alex lights a candle every 10 minutes. Each candle burns for 40 minutes before going out. How many candles are burning 55 minutes after he lit the first candle?
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Answer: C — 4
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Hint 1 of 2
List when each candle is lit and how long it stays burning.
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Hint 2 of 2
At minute 55, check which lit candles have not yet burned out.
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Approach: track burning intervals
- Candles are lit at minutes 0, 10, 20, 30, 40, 50, each burning for 40 minutes.
- At minute 55: the ones lit at 0 and 10 have gone out (out by 40 and 50).
- The ones lit at 20, 30, 40, 50 are still burning.
- That is 4 candles.
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