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April 28, 2015

April 28, 2015

Posted by **Word Problem** on Sunday, November 25, 2007 at 9:57pm.

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

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**Michael**, Sunday, November 25, 2007 at 10:00pmSet 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 37-cent stamps, and let y be the number of 20-cent stamps.

What two equations did you get?

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**Word Problem**, Sunday, November 25, 2007 at 10:01pmx+y=7.06

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**Michael**, Sunday, November 25, 2007 at 10:02pmThat'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?

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**Word Problem**, Sunday, November 25, 2007 at 10:04pm37x+20y=7.06

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**Michael**, Sunday, November 25, 2007 at 10:07pmThat'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?

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**Word Problem**, Sunday, November 25, 2007 at 10:09pmx+y=20

and

37x + .20y = 7.06

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**Michael**, Sunday, November 25, 2007 at 10:10pmGood. Our two equations are:

.37x + .20y = 7.06

x + y = 20

We're trying to find the number of 37-cent 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.

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**Word Problem**, Sunday, November 25, 2007 at 10:17pmWould the answer be D - 18 .37 stamps?

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**Michael**, Sunday, November 25, 2007 at 11:41pmYup. Nice job.

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