Problem Description
You have 12 balls that all weigh the same except one, which is either slightly lighter or slightly heavier. The only tool you have is a balance scale that can only tell you which side is heavier. Using only three weightings, how can you deduce, without a shadow of a doubt, which is the odd one out, and if it is heavier or lighter than the others?
P.S – I want you to try solving them before checking the solution. Do
share your logic & solutions in the comments. I’d love to see how
uniquely can someone think!
Assuming defective ball is heavier, divide the balls into 3 groups (4 balls in each).
1st pass:
Take first two groups and put them on the weighing machine.
If both are at the same level then we know that the heavier one is present in 3rd group
2nd pass:
Take 3rd group and divide it further i.e. 2 groups of 2 balls each and put them on the weighing machine
Take the heavier side group
3rd pass:
Now, we are left with only 2 balls so put them on the weighing machine and we can find the heavier one easily.