Question

There are 20 coins placed on a table such that tails is showing up. Suddenly electricity goes off and a boy sitting nearby inverts few coins and then he asks another boy to select some coins such that number of inverted coins is equal in every other subpart. He selects 8 coins and invert those 8 coins , and when electricity comes back he sees equal number of inverted coins in both subparts. Tell how many coins did first boy inverted.

Answer 1

At first the boy inverted 2 coins to heads.So when the other boy inverted the other 8 coins then the the number of heads was equal to numbers of tails i.e 10/10 each.

Answer 2

The 1st boy has inverted 2 coins, so when the 2nd boy inverted 8 coins , the no. of tails and heads became equal  i.e. 10 of  each.