Problem:

The problem is quite simple. You are given 8 identical-looking balls, one of which is heavier than the other 7 (all of which weigh the same).

Solution:

You can identify the heavier ball in only 2 weighings! The secret is not to get fooled into the “divide and conquer” approach where the input is halved in each iteration as explained above. To achieve this in only 2 weighings, you first put 3 balls in each bowl on the scale, e.g. {1,2,3} against {4,5,6}. Should the scale balance, you have only 2 balls remaining which you can compare by putting each in a separate bowl on the scale, e.g. {7} against {8}. Should the scale not balance, however, take the 3 balls from the heavier bowl on the scale (e.g. 1,2,3). Pick any 2 balls and compare these against each other, e.g. {1} against {2}. If the scale balances, you know it is ball 3 is the heavier. Is the scale moving, you know it’s the ball on the heavier side.

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