Heavy and Light Balls Puzzle

Puzzle:

You have 2 ball of each A,B,C colors and each color have 1 light and 1 heavy ball. All light balls are of same weight same goes for heavy. Find out weight type of each ball in minimum chances. You can use a two sided balance system (not the electronic one).

This puzzle was asked in many interviews – Drishti-soft, Yahoo, Infoedge.

Puzzle Solution:

Simply, you can check by taking 2 balls of same color. Now, comparing those balls with other balls but this will take 3 chances for each color type ball.

Answer is 2 chances.

So, Make a table for all conditions for all 6 balls that will help in understanding and solving this problem.

A1,A2,B1,B2,C1,C2

First weight A1,B1 and B2,C1 -> 3 cases equal ,left is heavy or left is light.

Case 1:
Equal, if equal weight simply B1,B2 will solve the problem.

Case 2:
If A1+B1 > B2+C1, then we know B1 > B2. Also just that A1>=C1.

Next compare A1,B1 and A2,C1
If A1+B1 = A2+C1 means A2 is heavy and A1=C1 light
If A1+B1 > A2+C1 means A2 is light and A1=C1 heavy
A1+B1 < A2+C1 will not happen because B1 is any way heavier.

Case 3:

If A1+B1 > B2+C1

Similar to above case we can check it.

3 Thoughts on “Heavy and Light Balls Puzzle

  1. sir this can’t be done in 2 moves.. we can’t determine it in two moves in case both the pairs are of equal wait. In this case though we can distinguish in two different groups but we can’t say which one will be heavy and which one will be light.

  2. Can you explain in the case 2, How can we say A1 is heavy ?

    B1 is heavy that’s sure.
    Now we may have the case like this ,
    A1 = Light
    B1 = Heavy
    B2 = Light
    C1 = Light

    So it will be HL = LL and make the left side heavy !

  3. pratik on July 4, 2015 at 4:16 pm said:

    @Sanjay,
    OK you do check grammar only…:D

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