Interview Question

Junior Field Engineer Interview(Student Candidate) Conway, AR

if you have 2 candles with wicks on both ends and 1 takes

  1 hour to melt completely, how do you tell, without measuring, when 45 minutes has passed

Interview Answer

2 Answers


Take one candle and light both ends. This will take 30 min. to burn through. When you light up both ends of that one candle, take the other candle and light one end of it. When the candle with both ends burns out, light the last remaining end of the second candle, This will take 15 min. to burn because half of the candle is already gone.

Mike on Mar 3, 2014

There is another option (although it's a bit quirky):

1) Line the 2 candles up so that they are parallel (like an equal sign)
2) Light the OPPOSITE ends of each candle
3) When the flames of the candles cross paths you have 30 minutes
4) Push one of the candles at one end (the unlit end) until it lines up with the other candle
5) When the flames of the candles cross paths again you have 15 minutes. 30+15 = 45. I prefer this scenario because you still have some candle left to use (for a harder problem), and you only need to light the candles once =D.

PTL on Jun 12, 2014

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