Question

Allen bought 20 stamps at the post office in 37¢ and 20¢ denominations. If the total cost of the stamps was $7.06, how many 37¢ stamps did Allen buy?

Set up a system of equations.
Then solve using substitution or elimination.

Answer 1

x + y = 20
.37x + .20y = 7.06

Answer 2

Those are your two equations

Answer 3

let a= number of stamps costing .37 and b=number of stamps costing .20
a+b=20
.37a+.20b=7.06

Answer 4

use substitution
a+b=20
a=20-b

Answer 5

.37(20-b)+.20b=7.06
7.4-.37b+.20b=7.06
7.4-.17b=7.06
-.17b=-.34
b=2

Answer 6

plug b back into one of the equations and solve for a.
2+a=20
a=18

he bought 18 stamps that cost 37 cents and 2 stamps that cost 20 cents

Answer 7

Let x=37 cent stamps
Let y=20 cent stamps

x+y=20
0.37x+0.20y=7.06

By using substitution you get:

y=20-x
0.37x+0.20(20-x)=7.06
0.37x+4-0.20x=7.06
0.17x=3.06
x=18

y=20-18
y=2

Therefore, there are 18 stamps at 37 cents and 2 stamps at 20 cents