You have a thousand Re. 1 coins with you. You have ten bags with you and you can put any number of coins in each of the bags. The condition is that if someone asks you for any amount between 1 and 1000, you must be able to give that amount by just giving the bag (you are not allowed to open the bag and give coins).
How will you do it ?
First Bag = 1 Coin
Second Bag = 2 Coins
Third Bag = 4 Coins
Fourth Bag = 8 Coins
Fifth Bag = 16 Coins
Sixth Bag = 32 Coins
Seventh Bag = 64 Coins
Eighth Bag = 128 Coins
Ninth Bag = 256 Coins
Tenth Bag = Remaining Coins.
Now think of any amount between 1 and 1000 and you will be able to give it by using bags (without opening them)
