You spend $30.40 on 4 cds. each cd costs the same amount and is on sale for 80% of the original price.

The original price is $9.5
In this question, you are given the total spending( $30.40), amount of spend (4CDs) and the discounted price(80%). Then to find the original price of the CD, the calculation would be:

Total spending = amount of cd x CD discounted price
$30.40 = 4 x 0.8 Original price
3.2 Original price= $30.40
Original price= $9.5