math
posted by dawn .
for every 8cds sold, there were 12 dvds sold. a combined total of 70 cds and dvds were sold. how many cds were sold that day? write a proportion to show the relationship and solve it to find the number so cds sold

d = (12/8) c = (3/2) c
or
d/c = 3/2
d + c = 70 so d = 70 c
so
(70 c )/c = 3/2
70  c = 3 c / 2
140  2 c = 3 c
5 c = 140
c = 28