coins puzzle

This is another coin puzzle. As per the puzzle you have 20 coin machines, each of which produce the same kind of coin. you know how much a coin is supposed to weigh. one of the machines is defective, in that every coin it produces weighs 1 ounce less than it is supposed to. you also have an electronic weighing machine. how can you determine which of the 20 machines is defective with only one weighing? (by one use, we mean you put a bunch of stuff on the machine and read a number, and that's it -- you not allowed to accumulate weight onto the machine and watch the numbers ascend, because that's just like multiple weighings). you are allowed to crank out as many coins from each machine as you like.


  1. assume wt of coin is 1 ounce and defective machine produce wt = 0.99 ounce

    noe take 1 coin from 1st machine 2 from 2nd machine and like that 20 from 20th machine .....
    and wt them
    assume 1+2+3+...20=x

    so if total wt is less than 0.1 by x then ans is 1 st machine

    if total wt is less than 0.2 by x then ans is 2nd machine

    like that :)

  2. @pappu your approach is correct..:)


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