If you don't believe that this works, try it!
Here is a table showing the possible coins that you could select for group one, and the resulting number of tails in group two:
Group One (10 coins) If you select: |
Group Two (90 coins) | |
---|---|---|
0 Tails | 10 Heads | 10 Tails |
1 Tail | 9 Heads | 9 Tails |
2 Tails | 8 Heads | 8 Tails |
3 Tails | 7 Heads | 7 Tails |
4 Tails | 6 Heads | 6 Tails |
5 Tails | 5 Heads | 5 Tails |
6 Tails | 4 Heads | 4 Tails |
7 Tails | 3 Heads | 3 Tails |
8 Tails | 2 Heads | 2 Tails |
9 Tails | 1 Heads | 1 Tail |
10 Tails | 0 Heads | 0 Tails |