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

8 Answers
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1-8 of  8
8 Answers
Top Voted Recent Answer
  • In one glass we measure 8minutes more to jet extra 1 min in better of another glass get 7 mins means 8+7  is  14.
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  • start both glasses. After it empties, turn the small glass, start time and continue watching the big glass. When, at the end of 11 minutes, the big one empties the small glass will be running for 4 minutes. Turn the big glass and wait another 11 minutes. 4 + 11 = 15. All it takes is 2 turns of the big glass. It's an absolute minimum.
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  • 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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  • so the best way to do is first we will start the hour glass one and when it ends after 11 minute we will flip it back. when it finishes we will start the hour glass two. after the end of hour glass two we can minus it from the the total of first to get the result.

    hour glass one =11 minutes 
    after flip=22 minutes 
    hour glass two=7 minutes
    final result=22 minutes-7 minutes
                    =15 minutes
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  • a·X - b·Y = 1 Let a = 11 and b = 7. It's immediately verified that the identity is satisfied by X = 2 and Y = 3. This suggests the following strategy: Start both glasses. When they become successively empty, turn the small glass, then the big one and the small one again. On its third run the small glass will empty 21 minutes from the start of the experiment. Start boiling your eggs at this point but do not yet turn the 7 min glass. After 1 minute (22 minutes after the beginning of the experiment) the big hourglass will become empty. Now, use the small glass twice to count 14 minutes. 1 + 14 = 15. In all, it will take 4 turns for the small glass and 1 turn for the bigger one.
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  • Let us again make use of the identity
    a·X - b·Y = 1
    Let a = 11 and b = 7. It's immediately verified that the identity is satisfied by X = 2 and Y = 3. This suggests the following strategy:
    Start both glasses. When they become successively empty, turn the small glass, then the big one and the small one again. On its third run the small glass will empty 21 minutes from the start of the experiment. Start boiling your eggs at this point but do not yet turn the 7 min glass. After 1 minute (22 minutes after the beginning of the experiment) the big hourglass will become empty. Now, use the small glass twice to count 14 minutes. 1 + 14 = 15. In all, it will take 4 turns for the small glass and 1 turn for the bigger one.
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  • with one flip i think there is no possible solution minimukm it taks two flips
     
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