Question 254371
A music store is selling compact disks for $11.50 and $7.50.
Let the number of disks of first type bought  = x
and the number of disks of second type bought = y
 Total number of disks  x+y = 12  ...(1)
Total amount   11.50x+7.50y = 110 ...(2)
(2)*2 =>        23x+15y     = 220 ...(3)
(1)*15=>        15x+15y     = 180 ...(4)
(3)-(4)=>                8x = 40 
                          x = 40/8
                          x = 5
(1) =>                  5+y = 12
                          y = 12-5
                          y = 7
Therefore the number of diks of price $ 11.50 = 5