Let "p" be the price you pay for each CD's
Since 4 CDs cost 30.40, the price you pay for each CD (p) is calculated as = total price for all CDs/ number of CDs
So, the price you pay for each CD (p) = 30.40/4 = $7.60
Since you paid 80% of the original price of each CD = 7.60/0.8 = $9.50
The price you paid for each CD = $7.60 per CD
The original price for each CD = $9.50