设10元有x张,则2元与5元的有﹙50-x﹚÷2 张
10x+﹙2+5﹚×﹙50-x﹚÷2=240
10x+7×﹙50-x﹚÷2=240
10x+175-7/2x=240
13/2x+175=240
13/2x=65
x=10