Time Measurement


How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

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  • 2 Answer(s)

    Use 7 and 11 after 7 passed start measuring after 11 passed upturn it and continue measuring

    Yodha Expert Answered on 11th June 2022.

    What do you mean by “… after 7 passed start measuring after 11 passed”?

    on 12th June 2022.

    after 7 minute hour glass sand settled down
    thats what i mean

    on 14th June 2022.

    “after 7 passed start measuring … ” Start measuring what??

    on 14th June 2022.


    on 16th June 2022.

    That I know! But you said “after 7 passed start measuring…’. Do you mean to say that you were not measuring  till then? Also, you said ‘start measuring’ – how? Using the 11? In that case, you will end up with 7 + 11 = 18 min.

    on 17th June 2022.

    we ignore the time passed till then and then start measuring it.if u start measuring when 7 passed after both 11 and  7 were used  and total time u will measure will be the time of remaining sand  in hour glass  of  11  =4 minutes and after  upturning 11  again  after the  sand settled  =11 minutes
    4+11 = 15

    on 17th June 2022.

    The question doesn’t provide for “ignoring” any timeframe.  You can’t arbitrarily insert ‘gaps’ as per convenience.

    on 17th June 2022.

    I didn’t inserted gaps I started late pls this is too foolish if you can’t see this after so much explanation. The question didn’t state you have to start measuring now

    on 18th June 2022.

    “Starting late” has the drawback that it won’t work when required immediately. e.g. If someone says ‘I am going to the store to get something.  If I don’t return in 15 min., you should come to my help.’ In this situation,  you can’t use your method to measure the time. 


    What your method actually measures is 22 minutes, NOT 15 min. as required in the question because before starting ‘your‘ measurement, you have actually ‘measured’ 7 minutes (because you waited till the 7-min glass drained out). even though you chose to ignore it. (Had you started measuring while the7-min glass was running, you could have claimed that you didn’t measure the time before starting, because you don’t know how much time had passed before you started.)  

    on 19th June 2022.

    Because you do not understand a simple thing we have to measure 15 minutes it does not say now it is a question not a life problem you have thought about the use of the problem unnecessarily or its your grudge against me

    on 19th June 2022.

    When somebody asks someone to measure something, it implies that the measurement should be done when asked and not after some random time as per the other person’s convenience. If I were a nurse and you, a doctor (or my colleague), and you asked me to measure a patient’s temperature / BP, I would do it immediately when asked (unless specifically asked to wait for ‘x’ minutes) and NOT after, say, half an hour (at my convenience), claiming that you didn’t say ‘measure it now / immediately‘. As simple as that.

    on 20th June 2022.

    it is not a life problem but a puzzle  if your are too dense then i cant help sorry

    on 21st June 2022.
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    Start both the 7-min and 11-min glasses simultaneously. After the 7-min one runs out, turn it upside down and let it continue to run. By the time the 11-min glass runs out (11 min. passed), the 7-min. glass will have run for 4 min. after it was upturned first. Turn it upside down again and continue. It will run out in the next 4 min. , completing 15 min.

    Viji_Pinarayi Expert Answered on 12th June 2022.

    u didnt need to think this much

    on 14th June 2022.
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