Correct Answer - Option 1 : 2
Explanation:
Divide 9 bags into three parts.
2,2 and 5 respectively.
If we compare the 2,2 bags on pans of a balance.
We can identify which side is the lighter bag placed.
And then we will need only one more weighing for identifying the faulty bag.
So only two weighings are required.
Alternative solution:
In the case of a weighing balance (i.e. beam balance) the following model can be observed.
1 - 3 → 1 weighing required
4 - 9 → 2 weighings required
10 - 27 → 3 weighings required
28 - 81 → 4 weighings required
And the process will go so on.
As there are nine objects. The minimum number of weighings required will be only 2.