Creative Thinking: Test Yourself with Tough Interview question (mathematic)

This is one of the tough interview questions which I have found. It will basically test your logic thinking and lateral thinking skills via mathematic approach. The question is:

If you got 8 balls, one of them has 9.8g and the remainders are 10g,

You are given one balance. What is the minimum try needed for you to find out the 9.8g ball?

ANSWER:

Minimum try is two only.

Explanation:

1. Separate 8 balls into 2 groups, 6 balls and 2 balls, respectively. Putting the first group in three to three balls arrangement in the balance for its first try.

2. If the first group is unbalance, the second group is surely in balance. Then process to test the less weight part of the balance by using one to one ball arrangement in the balance for its second try then you know which one have different weight.

3. However, if the first group is balance, then what you need to do is just test the second group for the second or last try.