Jason has 43 stamps. Some

are worth 15 cents and some

are worth 20 cents. If their total

value is $7.50, how many of

each kind does he have?

Jason has a total of 43 stamps, and we have two different stamps involved.

x = 15 cents

y = 20 cents

We will need to set up two equations and then use substitution:

43 = x + y (represents total stamps)

7.50 = 0.15x + 0.20y (represents total value)

To use substitution, we'll use the first equation and get either x or y on its own. In this case I will choose to get y on its own:

43 - x = x - x + y (subtract x to get y alone)

43 - x = y

Now we will use this in the second equation and simplify:

7.50 = 0.15x + 0.20 (43 - x)

7.50 = 0.15x + 8.6 - 0.20x

7.50 = 8.6 - 0.05x

-1.1 = - 0.05x (divide by - 1.1 to get x alone)

22 = x

Now that we know Jason has 22 of the stamps that are worth 15 cents, we need to find y by plugging x, 22, into the first equation:

43 = 22 + y

21 = y

Jason has 22 stamps that are worth 15 cents and 21 stamps that are worth 20 cents.