Question

You have nine identical balls and among them, one is defective as it weighs more than the rest. You are provided with a physical balance.
The minimum number of times you should use the physical balance to figure out the defective ball is?

• A. 11
• B. 5
• C. 2
• D. 7

Answer 1

The correct option is C 2

Let's try to solve this in simple steps:

Step 1: Segregate all 9 balls in three sets of 3. Now weigh any two sets against each other. If both are equal in weight then the third set has the heavier ball. If they are unequal in weight, the heavier side of the two sets has the heavier ball. Now take the heavier set of the three and discard the other 6 balls.

Step 2: Take any two balls from the set and weigh them against each other. If both are of equal weight then the third ball is the heavier ball. And if they are of unequal weight, the heavier side of the two is the heavier ball.
Hence, by using the physical balance twice, you can find out the heavier ball.