I have 2 hour glass one measures 11 minute and another measures 7 minute. how u measure 15 minutes? using only one flip of any one of hour glass.

only one flip is allowed

Your Answer

thanks evangeline for a2a.

The question has a mistake in it because there is no possible solution when there is one flip however it  is possible with the following flips. Let the 11 hour glass is 1st and 7 hour glass is 2nd.
 Start both the hour glasses at the same time and at 7th minute the 2nd hour glass is empty so flip(flip number 1) it , at 11th minute the 1st hour glass will be empty so flip it (flip number 2), after 14 minutes the 2nd hour glass will be finished and should be flipped again(flip number 3), now after completion of 21st minute the second hour glass will be empty again but the first hour glass has still 1 minute remaining to finish , i.e. 22 minutes, so let’s count our fifteen minutes from the end of 21st minute hence after 22nd minute we have counted 1 minute at this moment flip the second hour glass 2 times(flip number 4 and 5) in order to calculate the remaining 14 minutes.
So total min. number of flips required to calculate 15 minutes will  be 5.
 

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