Math
posted by Mary on .
A dress costs $60. A skirt costs 25% less. M bought some skirts and dresses for $2220. 70% of the items were dresses. Rest were skirts. How much do skirts cost? (All the skirts together.)

D*60 + S(60*.75)=2220
.7(D+S)=D
Can you take it from here? 
$2220 = 60*D + 45*(3/7)D
Solve for D, the number of dresses.
(3/7)D is the number of skirts bought, since 30% were skirts and 70% dresses. $45 is the cost per skirt.
Solve for D. (It should be an integer). Multiply that by $60 for the amount spend on dresses.
I get $1680.