# Defective stack of coins puzzle

There are 10 stacks of 10 coins each.

Each coin weights 10 gms. However, one stack of coins is **defective** and each coin in that stack weights only 9 gms.

What is the minimum number of weights you need to take to find which stack is defective? How?

**SOLUTION-** 1 Measurement Only

**EXPLANATION-**

We will take,

1 coin from the first stack,

2 coins from the second,

3 from the third

and

so on.

In total we will have 55 coins.

If all of them were non-defective, they would weigh 550 gms.

If stack 1 is defective, the measure would read 549 gms.

If stack 2 is defective, you will read 548 gms.

and so on.

So by taking **one measurement** you can identify, which is the defective stack.

### Your Answer

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