Question : Here is a very intellegent blind man. He was asked to do the following problem and he did it. Can you do it? Of course you have to assume that you are blind too!
On a table 100 coins have been placed. 10 of them are showing heads while 90 others are showing tails(none of the coins is standing). A blind man is told to divide the 100 coins into two groups such that the number of coins showing heads in both the groups is the same. The blind man thinks for a short while and says “I see….” and does the job. How does he do it?
Hints:
1. The no. of coins in the two groups need not be the same.
2. The coins can be flipped.
Answer : Select any 10 coins from the 100 and flip all the 10. Now you will have two groups: one with 90 coins and the other with 10 coins.
Suppose that out of the 10 selected coins, 4 had heads. This means that out of the ramaining 90, 6 have heads. Now after flipping, the other group will also have 10 – 6 = 4 number of heads!
You can see for yourself that this works for all cases.