Answer or Solution :
1. This "10 Bag of Coins" puzzle is an interesting job interview puzzle.
2. We know that the coins in the forgery bag weigh 1.1 gms each and the coins in rest of the bags weigh 1 gram each.
3. As there are random number of coins in each bag, weighing each bag will show different readings.
4. Now just sharpen your analytical skills and narrow down your investigation by taking samples from each bag.
5. If you weigh one sample from each bag, you need to weigh more than once to determine which bag contains the forgery coins, considering that the 1st bag is not forgery bag.
6. But we can find out the forgery bag in just one time weighing (reading) on the electronic weighing machine.
7. Take 1 coin from 1st bag, 2 coins from 2nd bag, 3 coins from 3rd bag, so on and 10 coins from 10th bag.
8. Now you have a total of 1+2+3+4+5+6+7+8+9+10=55 coins.
9. Weigh all the coins together using the electronic weighing machine.
10. Check the decimals in the reading.
11. As the forgery coins weigh 1.1 grams each, the coins from that bag should provide readings in decimals.
11. If the decimal reading shows 55.1->1st bag contains forgery coins as there are only 1 coin from the 1st bag in the sample.
12. If the decimal reading shows 55.2->2nd bag contains forgery coins as there are two coins from the 2nd bag in the sample.
13. Similarly .3->3rd bag, .4->4th bag, .5->5th bag, .6->6th bag, .7->7th bag, .8->8th bag, .9->9th bag
14. But if the decimal reading shows 56.0, then the 10th bag is the forgery one as we have 10 coins from that bag and ten .1 gram increases the total weight by 1 gram.