posted by Cat .
On a Christmas package, Audrey needs to use only 40-cent stamps and 16-cent stamps. If she uses twice as many 40-cent stamps as 16-cent stamps, how many of each type of stamp must she use to mail a package costing $5.76 in postage?
Let x = .16 stamps and y = .40 stamps.
y = 2x
.16x + .40y = 5.76
Substitute 2x for y in second equation and solve for x. Insert that value into the first equation and solve for y. Check by inserting both values into the second equation.