A postal clerk sold some 15 cent stamps and some 25 cent stamps. Altogether, 15 stamps were sold for a total cost of $\$3.15$. How many of each type of stamp were sold?
+128399 Let the number of 15 cent stamps = x
Let the number of 25 cent stamps = 15 - x
So
15x + 25 ( 15 - x) = 315
15x + 375 - 25x = 315
15x - 25x = 315 - 375
-10x = - 60 divide both sides by -10
x = 6 = the number of 15 cent stamps sold
15 - x = 15 - 6 = 9 = the number of 25 cent stamps sold
