Sir, the solution you gave is a bit confusing. Suppose we take out 20 coins which contains 17 tails and 3 heads and then we flip all the coins as you said in the solution. Then there will be 17 heads and 3 tails.now how can we divide these 20 coins into 2 piles having equal no. of tails. since we do not know which coin is head or tail we cannot flip that coin to get even no. of head and tails and also we cannot guarantee that each pile will have equal no. of tails.
Puzzle-Infinite quaters
@Shivank97 In the question it is already given that there are a total of 20 tails. So if you separate any 20 coins. And say if in that 20 coins 17 are tails and 3 are heads. Then in the remaining coins only 20-17 ie. 3 tails would be there. No if you flip all the coins in that 20 coins, you will get 17 heads and 3 tails. Which is same as the number of tails in the remaining coins.
Hope you understand 
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thankyou sir. i got it now.