The best deal would be "three for the price of two" since buying one and 25 percent off would be 17.5 plus 10 for a third one is 27.5 compared to 20 for 3
He buyed 240 cards because
20
x
12
-----
40
+
20
-------
240
6/y=9/5(due to similarity)
y=6*5/9=30/9=10/3=3.333..
