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.
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After going through the question I consider the following two cases.
1. Since the other boy inverted 8 coins and there are equal number of inverted coins in both sub-part, the first boy inverted 8 coins also. Therefore there are 4 coins remain in the original place.
2. If we consider that the coins are placed in two equal sub-parts then it has to be 10 coins in each part. Since the other boy inverted 8 coins therefore the first boy inverted (10-8)=2 coins only.
1. Since the other boy inverted 8 coins and there are equal number of inverted coins in both sub-part, the first boy inverted 8 coins also. Therefore there are 4 coins remain in the original place.
2. If we consider that the coins are placed in two equal sub-parts then it has to be 10 coins in each part. Since the other boy inverted 8 coins therefore the first boy inverted (10-8)=2 coins only.
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