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Measure by Hourglass

Can you clock the boiling of an egg for seven minutes, with a 9-minutes, 11-minutes and 14-minutes hourglass? If yes, then within how many minutes you can do this?


Answer: 1

16 minutes. Start all the hourglasses together. When the sand stops running in the 9-minute hourglass, the 11-minute hourglass will have 2 minutes remaining whereas the 14-minute hourglass will have 5 minutes remaining. Now, turn the 14-minute hourglass on its side and simultaneously drop the egg. When the sand stops running in 11-minute hourglass, straighten the 14-minute hourglass. Thus, the whole process takes just 16 minutes.

Answer: 2

18 minutes. Start all the hourglasses together. When the sand stops running in the 9-minute hourglass, turn the 14-minute hourglass over. When the sand stops running in 11-minute hourglass, turn again the 14-minute hourglass and simultaneously drop the egg. When the sand stops in the 14-minute hourglass, seven minutes will have elapsed. Thus, the whole process takes 18 minutes.