Eric purchased three music cds and a sweatshirt from a band's online store and received a 20% discount. he paid $100 for his purchase. the following week, the same store offered a 40% discount on all its products. eric's friend neil took advantage of the sale and bought four music cds and two sweatshirts for $120.

1. assuming that the actual prices of the music cds and the sweatshirts are unchanged, the price of a music cd is $
answers:
20
25
30
50

and the price of a sweatshirt is $
answers:
20
25
30
50

(3c+s)(100-20)/100=100  multiply both sides by 100

(3c+s)80=10000  divide both sides by 80

3c+s=125  subtract 3c from both sides...

s=125-3cnow let's look at the second situation...

(4c+2s)(100-40)/100=120  multiply both sides by 100

60(4c+2s)=12000  divide both sides by 60

4c+2s=200  divide both sides 2

2c+s=100 subtract 2c from both sides

s=100-2c, and from earlier we saw that s=125-3c, since s=s:

100-2c=125-3c  add 3c to both sides

100+c=125  subtract 100 from both sides

c=25, and since s=100-2c

s=50

So cds cost $25.00 and sweatshirts cost $50.00