break down the numbers 64, 40, and 32 to find a common number.
64
32
16
8
4
2
40
20
10
8
5
32
16
8
4
2
In all three, there is a common number of eight.
Therefore (answer):
There would be 8 cards in each pile.
8 piles of basketball cards, 8 cards per pile.
5 piles of football cards, 8 cards per pile.
4 piles of baseball cards, 8 cards per pile.
I hope I explained this good enough. Please comment with any questions you may have on how I got this answer.