Solving This Interview Puzzle is IMPOSSIBLE Unless You Find The Trick!

Can You Solve It?

Today, we’re going to take a look at a puzzle said to be asked in the legendary Google Interview rounds! Here it is…

Shoot your shot at this tricky puzzle! (IMAGE SOURCE)

There are 12 men on an island, and one of them has a different weight from the rest. The problem is that you do not know whether he is heavier or lighter.

All you have is a balance scale, and you are only allowed to use it 3 times. There are no digital numbers and no exact measurements.

Each weighing can only give you one of three results: the left side is heavier, the right side is heavier, or both sides balance.

Now, to solve this puzzle, we must answer the question…

Can you find the odd man out in just 3 weighings?

Now, before you scroll down to reveal the solution, I recommend that you really think about this problem.

Solution

Do you have your answer yet? Well, here’s the way I solved the puzzle…

First of all, label the men A, B, C, D, E, F, G, H, I, J, K, L.

First weigh A, B, C, D vs E, F, G, H.

If they balance, the problem is very simple. The odd man is one of I, J, K, L.

Now weigh I, J, K vs A, B, C. Since A, B, and C are normal, this tells you everything. If it balances, L is odd. Weigh L against a normal man to see if he is heavier or lighter.

If IJK is heavier, then one of I, J, K is heavy.

Weigh I vs J.

If one is heavier, that is the answer. If they balance, K is heavy. If IJK is lighter, same idea, but the odd man is lighter.

Now, suppose the first weighing doesn’t balance.

Let’s say ABCD is heavier than EFGH…

That means the odd man is either A, B, C, or D and heavy or E, F, G, or H and light. Now weigh A, B, E vs C, D, F

If ABE is heavier, the answer is either A heavy, B heavy, or F light. Weigh A vs B. If one is heavier, that’s him. If they balance, F is light.

If CDF is heavier, the answer is either C heavy, D heavy, or E light. Weigh C vs D. If one is heavier, that’s him. If they balance, E is light.

If they balance, then A, B, C, D, E, and F are normal. So the odd man is either G or H, and he is light.

Now, weigh G vs H. The lighter one is the answer.

And if the first weighing goes the opposite way, just flip heavy and light and use the same logic.

And that’s it! This puzzle makes you feel like you have to weigh 12 different people, but in reality, you don’t :)

Could you figure out a different method to solve this puzzle? Let me know in the comments section!