Physical balance
Probability
Level
pending
You have 81 identical balls of same colour, size and shape. Out of these 81 balls there is an odd ball which weighs little more than other balls. In how many trials can you find the odd ball?
The answer is 4.
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1 solution
Put 2 7 balls on each side of the balance and keep 2 7 aside.
Now, 2 cases arise:
Either the weights will balance or one side will be heavier than the other.
If they balance then take the 2 7 balls that were kept aside or else, take the balls that weighed more.
Now, put 9 on each side and keep 9 aside.
Follow similar method as previously mentioned and put 3 on each side followed by 1 on each side, and we will successfully have determined the heavier ball.