Posted by Word Problem on .
Can someone please help with this?
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?
A) 15
B) 16
C) 17
D) 18

Algebra 
Michael,
Set up a system of equations to model this situation. (Note that a system of equations is TWO different equations.)
Let x be the number of 37cent stamps, and let y be the number of 20cent stamps.
What two equations did you get? 
Algebra 
Word Problem,
x+y=7.06

Algebra 
Michael,
That's only one equation.
Anyway, the number of stamps that he buys is 20.
The other equation will deal with the stamp prices.
What do you get? 
Algebra 
Word Problem,
37x+20y=7.06

Algebra 
Michael,
That's close. The stamps are in CENTS, though.
.37x + .20y = 7.06
That is one equation. The other equation deals with how many stamps he bought. What is it? 
Algebra 
Word Problem,
x+y=20
and
37x + .20y = 7.06 
Algebra 
Michael,
Good. Our two equations are:
.37x + .20y = 7.06
x + y = 20
We're trying to find the number of 37cent stamps (x). We can solve this system of equations by substitution. Solve the second equation for y, and then plug that into the first equation.
We now only have x's in the equation, so solve it as you would any other equation. 
Algebra 
Word Problem,
Would the answer be D  18 .37 stamps?

Algebra 
Michael,
Yup. Nice job.