so all four went to the ice-cream lady and got first 2 ice-creams, the lady said, "ok 4 bucks for the first one, and half-off the second, or 2 bucks".
so, for the first two cones, they didn't pay 4+4 bucks, they only paid 4+2 bucks, and for the next two cones, they paid the same.
so in total for the four cones they paid 4+2 and 4+2, or 12 bucks.
how many times do 4(boys) go into 12(total)? 12/4.