Given 9 ball all of which weigh the same except for one, what is the minimum of weighings necessary to find the ball weighs more (or less)?

Question

Accepted Answer

Answer - Three

1) Take 8 ball and place 4 ball on each side of a scale.

If the scale is balanced, it means the 9th ball is lighter than the others.

If the scale is unbalanced, it means one of the sets of 4 ball is lighter.

If the scale is unbalanced, select the set of 4 ball that is lighter.

2) Take the 4 ball and divide them into 2 pairs of 2 ball each.

Weigh the two pairs of ball by placing one pair on each side of the scale.

The lighter ball is in the set that caused the imbalance.

3) Finally, take the two ball from the lighter set (the one causing the imbalance) and weigh them against each other.

The lighter ball will be identified as it will cause an imbalance on the scale.

Accepted Answer

9 times the one ball's weight then compare to the overall weight of all 9 together

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