Puzzle 27 | (Hourglasses Puzzle) Last Updated : 19 Jan, 2023 Improve Improve Like Article Like Save Share Report Puzzle: Given two hourglass of 4 minutes and 7 minutes, the task is to measure 9 minutes. Solution: At 0 minutes: Start both hourglasses at the same time. At 4 minutes: 4 minutes hourglass runs out and flip it. 7 minutes hourglass is left with 3 minutes. At 7 minutes: 4 minutes hourglass is left with 1 minute. 7 minutes hourglass runs out and flip it. At 8 minutes: 4 minutes hourglass runs out and 7 is filled with 6 minutes and 1 minute on the other side. Flip it as the sand is left with 1 minute. At 9 minutes: 7 minutes hourglass becomes empty from above side. Hence we measured 9 minutes. Like Article Suggest improvement Previous Puzzle 12 | (Maximize probability of White Ball) Next Puzzle 17 | (Ratio of Boys and Girls in a Country where people want only boys) Share your thoughts in the comments Add Your Comment Please Login to comment...