Question

Jennifer went to the post office for stamps. She bought the same number of 8-cent stamps and 10-cent stamps. She also bought as many 2-cent stamps as both of the other two kinds combined. How many of each kind did she get if she paid a total of $4.40 for them all? Due today! IM SO CONFUSED

Answer 1

Write it out as a set of equation:
Let x be number of 8 cent stamps, y be 10 cent stamps, and z be 2 cent stamps.
x=y
z=x+y
8x+10y+2z=440
Lets first solve for x:
from x=y and z=2x(from first equation) the last equation is
8x+10x+4x=440
22x=440
x=20
know that x=20, you also know that y=20 as well, since z=x+y, z=40.
So 20 8-cent stamps, 20 10-cent stamps, and 40 2-cent stamps.

Answer 2

x=number of 8-cent stamp=number of 10-cent stamp
y=number of 2-cent stamp.
$4.40=400 cents

She bought the same number of 8.cent stamp and 10 -cent stamps, she also bought as many 2-cent stamps as both, therefore:
x+x=y  ⇒2x=y
We can suggest this system of equations:

2x=y
8x+10x+2y=440

We can solve this system of equation by substitution method.

8x+10x+2(2x)=440
8x+10x+4x=440
22x=440
x=440/22
x=20

y=2x
y=2(20)=40

Answer: She bought 20 stamps of 8 cents, 20 stamps of 10 cents, and 40 stamps of 2 cents