Steem Riddle of the Week #2: Flipping Cards answer revealed

Riddle #2 went unsolved

Despite a 2SBD bounty, no one was able to correct answer last weeks riddle. So I'm going to write up the answer. For those of you who missed last weeks riddle, you can check out the problem at the link below. Warning, the answer is spoiled below.

https://steemit.com/life/@droopy/steem-riddle-of-the-week-2-flipping-cards-prize-doubled

Solution

Pick 10 cards and random and form them into one pile. The remaining 42 cards are the second pile. Flip the entire 10 card pile over. The two piles are now guaranteed to have the same number of fave up cards.

Why?

Well suppose our 10 card pile initially had X face up cards in it. This means that the 42 card pile has 10-X face up cards in it. When we flip the entire 10 card pile over, it now has X face down cards and 10-X face up cards. Thus no matter what X was we have 10-X face up cards in both piles.

This answer is tricky to see, but if you imagine doing it (or try it a few times with a real deck of cards) you can see it works.

Stay tuned for riddle 3

I'll be posted riddle #3 tomorrow with a 1SBD prize for the first correct answer, be sure to follow me so you can start solving right away.