16 August 2007


You have 5 boxes and each box has 5 marbles in it. Marbles in 4 bags weight 10g each and in one bag weight 9g each. You don't know which bag has 9g marbles and you are given a chance to use a weight scale for one time. How can you find the bag with 9g marbles?

For Solution SCROLL DOWN...


Number the bags from 1 through 5. Take 1 marble from bag 1, 2 marbles from bag 2, 3 marbles from bag 3, 4 marbles from bag 4 and 5 marbles from bag 5. Now put them on the weightscale. Now there are 5 possible measurements. If all marbles would weigh 10g, the total would be 150g. But one or more marbles weigh 9g. So if you took one 9g marble, the total would be 149g. If you took two 9g marbles, the total would be 148g. And so on.

Therefore, 150-(Measured Weight) gives the bag number which contain 9g marbles.
(Ex: If measured weight is 147g, 150-147=3 is the bag number as you have taken three 9g marbles from bag number 3)


jayantchauhan said...

1. Label the boxes Bx ,s.t. x : 1-5
2. Pick x number of balls from Bx.
3. Sum = weight of all these balls collected.
4. Diff = (1+2+3+4+5)*10 - Sum
5. The box containing 9g balls is
Bx : x=Diff
Thats it :)...

vijay said...

place 1 bag each on d balance tray........if any side goes contains the 9g bag.......if no another 1 each on both side.......and check again............if no change ........then the 5th bag is the wanted 1..........rite??

kumar said...

take 1 marbel from 1st bag
2 from 2nd 3 from 3rd 4 from 4th and 5 from 5th
now weigh them
if it is 1 less than 150 then it is 1st 2less then 2nd 3 less then 3rd.....