10 identical bottles of pills

This is a very popular brain teaser with many companies.

Problem :

We have 10 identical bottles of identical pills (each bottle contain hundred of pills). Out of 10 bottles 9 have 1 gram of pills but 1 bottle has pills of weight of 1.1 gram. Given a measurement scale, how would you find the heavy bottle? You can use the scale only once.

Answer: 

First, arrange the bottles on shelf and now take, 1 pill from the first bottle, 2 pills from the second bottle, 3 pills from the third bottle, and so on. Ideally you would have (10)*(11)/2=55 pills weighing 55 grams, when you put the entire pile of pills on the weighing scale.The deviation from 55 g would tell you which bottle contains the heavy pills.

If it is .1 gram more, it is 1st bottle which has heavy pill, if it is .2 more, gram 2nd bottle has heavy pills, if it is .3 more, gram 3rd bottle has heavy pills.

12 Thoughts on “10 identical bottles of pills

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  3. Simply place all 10 bottles on the scale and remove 1 at a time until the remaining weight reduces by the net weight of 1 x bottle plus 110 grams.

  4. JHALAK JAIN on September 26, 2016 at 12:02 pm said:

    nice logical question

  5. Shahbaz Khan on December 27, 2016 at 5:30 pm said:

    Divide 10 bottles into group of 2 (5 bottle each) Now wight them now take out the group which is more in wight. Repeat the process until you found the heavier bottle. It will take less number of comparision.

  6. Shahbaz Khan on December 27, 2016 at 5:30 pm said:

    Divide 10 bottles into group of 2 (5 bottle each) Now wight them now take out the group which is more in wight. Repeat the process until you found the heavier bottle. It will take less number of comparison.

  7. Ravi Kumar H M on May 31, 2018 at 6:26 pm said:

    What if 10th bottle has the pills weighing 1.1gm?
    10*1.1 = 11
    45+11=56gm – How will you identify?

    • Deepak on August 31, 2018 at 10:04 pm said:

      In case Bottle 1 is heavy then the final weight would be 55.1
      for second bottle 55.2 and for tenth bottle 56. So it will be 10th bottle
      1st 55.1
      2nd 55.2
      and so on

      9th 55.9 and
      10th 56.

  8. Rushabh on March 27, 2020 at 5:17 pm said:

    Actually, I was confused about the measurement scale before seen answer.
    But if I consider level scale instead of weighing scale it may be easy to find out, if m not wrong. How:?
    The answer is if the pills weight is more, then definitely on level scale its bottle level height is low compare to others (but in minor, but remaining all bottles level is same).
    as per density rule, but before that we have to tapped accurately and I think its no need to measure by scale also.
    we can identified by visually.

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