30 Minute Puzzle – Sand watches

30 Minute Puzzle
Here is another riddle like we earlier had with the Burning Rope timer with a different concept and sure a good one!!
Lets move right away to the brain teaser:

You are given two “hourglasses(sand watches)”, one of which will empty in 9 minutes, and one in 13 minutes. You need to measure a time interval of exactly 30 minutes. Is it possible?

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2 Responses

  1. Jyoti says:

    yes its possible….. the trick is 30=13+13+(13-9)

    so start with 13min and 9 min glass together…start to measure the time after 9min glass get finished… in this way u get 4 min then use 13 min glass twice to measure the rest 26 min

    cheers

  2. Akshat says:

    Start both of them. As soon as the 9 min glass finishes , reverse it and wait for 13 min glass to finish . Now as 13 min glass is over stop the 9 min glass.In this way you get the 4 minutes time in 9 min glass and have already used 13 min of your time. Now turn 13 min glass again , and as it finishes , use 4 min time reserved in 9 min glass. You get your 30 min . Eureka !!!!

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