A brain teaser: There are 10 coin-producing machines. The weight of each coin they produce is 10 grams. One of them has a fault and starts producing 9-gram coins. We have to weigh just once and find out which machine is that. JUST ONCE.
We can take as many as coins from any number of machines and weigh the weight of the coins taken.

Question

A brain teaser: There are 10 coin-producing machines. The weight of each coin they produce is 10 grams. One of them has a fault and starts producing 9-gram coins. We have to weigh just once and find out which machine is that. JUST ONCE.
We can take as many as coins from any number of machines and weigh the weight of the coins taken.

aravindg · Answer

100 grams

anonymous · Answer

Take 1 coin from the first machine. 2 from the second......and so onn..

parthkohli · Answer

@siddhantsharan Well done ^_^ can you explain so others understand how?

anonymous · Answer

Well. 
Let's take 1 coin from machine 1. Two from machine 2. 3 from 3 and sooo onn. right up till  10 from Machine 10.
Now, Lets weigh it.
So we know that the weight should have been 10 + 2(10) .....10(10) = 550 grams.
But due to one of the machine it isnt. Lets subtract the weight of the coins we weighed from that 550. You should be able to figure it out from here.

parthkohli · Answer

Very well done!

anonymous · Answer

Thanks :).