48 people each go 8 times, * * need to go 48*8=384 (person-times). If everyone buys X cards every time they go to X, the number of withdrawals is 384/x (times), and if the total expenditure is Y, there is y=40*384/x+240x. There is a minimum value if and only if 40*384/x=240x. If x=8, you can buy 8 cards, and the minimum value of y is √.