On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

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Friend 2 must have taken top 15 cards from the pile and reversed them. Now there are two piles, one with 15 cards and one with 37 cards and both of them will obviously have the same number of inverted cards.If you want to understand mathematically, let us say that there were x inverted cards in the top 15 cards of the deck. Then the remaining 37 cards will comprise of 15-x number of inverted cards.

If we reverse the 15 cards the number of inverted cards will become 15-x and the number of inverted cards will be same in both the piles.