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Interview Question

Interview(Student Candidate)

There are 8 balls that look the same. 1 of these balls is

  heavier than the rest. WIth a double scale, how would you find the heaviest ball?

Interview Answer

3 Answers


split the 8 balls into 2 groups of 4. weight each group on each side of the scale. Discard the lighter side. Take the heavier group and split into 2 groups of 2. Discard the lighter side. Take the heavier group and split into 2 groups of 1. the heavier side is the heaviest ball.

Interview Candidate on Feb 13, 2013

You split the balls in 3 groups - 3, 3, 2. 1st weigh. On each side of the scale place 3 balls. - If he groups are equal in weight, then w)eigh the 2 balls from the 3rd group => you'll have your answer in 2 steps (2nd weigh) - If the 3-ball groups are not equal in weight, pick the heaviest. 2nd weigh: on each side of the scale place one ball from the previously chosen group of 3. - if the balls are equal, the heaviest is the one that is left -otherwise, the scale will tell you which ball is heavier. Thus, you use the scale only 2 times. This is the minimum number of operations that has to be done.

Alexandra on Feb 14, 2013

Split into 3,3,2 say a3,b3,c2 take a3,b3 [1st weigh] Now there are 2 possibilities: 1) if equal then goto c2 and weigh those 2 to know the heavier one [2nd weigh] 2) say a3 is heavier now weigh 2 (say x and y)out of the 3 (say x,y,z)of them [2nd weigh] Now again 2 possibilities -if equal the 3rd left one ie z is the heaviest -if one say x is heavier than y, then that is the heaviest one! HENCE we need to weigh 2 times.

Sowmya on Aug 15, 2013

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