Answer:
Cost of 1 DVD is $6.5
Cost of one CD is $4.5
Combine cost of one DVD and CD is $11
Step-by-step explanation:
Given :
Kate bought 3 used CDs and 1 used DVD at the bookstore.
Her friend Joel bought 2 used CDs and 2 used DVDs at the same store.
Kate spent $20
Joel spent $22
To Find : the cost of a used CD and a used DVD
Solution :
Let cost of 1 used CDs be $x
Let cost of 1 used DVDs be $y
Cost of 3 used CDs = $3x
Cost of 2 used CDs = $2x
Cost of 2 used DVDs = $2y
Kate bought 3 used CDs and 1 used DVD at the bookstore.
She spent $20
So, equation becomes :
⇒
---(a)
Joel bought 2 used CDs and 2 used DVDs. she spent $22.
So, equation becomes:
⇒
--(b)
Now solve (a) and (b) to determine the value of x and y
We will use substitution method
Substitute the value of x from (b) in (a)
![3(\frac{22-2y}{2} )+y=20](https://tex.z-dn.net/?f=3%28%5Cfrac%7B22-2y%7D%7B2%7D%20%29%2By%3D20)
![33-3y+y=20](https://tex.z-dn.net/?f=33-3y%2By%3D20)
![33-2y=20](https://tex.z-dn.net/?f=33-2y%3D20)
![33-20=2y](https://tex.z-dn.net/?f=33-20%3D2y)
![13=2y](https://tex.z-dn.net/?f=13%3D2y)
![\frac{13}{2} =y](https://tex.z-dn.net/?f=%5Cfrac%7B13%7D%7B2%7D%20%3Dy)
![6.5 =y](https://tex.z-dn.net/?f=6.5%20%3Dy)
Thus cost of 1 DVD is $6.5
Now substitute this value of y in b to get value of x
⇒![2x+2(6.5)=22](https://tex.z-dn.net/?f=2x%2B2%286.5%29%3D22)
⇒![2x+13=22](https://tex.z-dn.net/?f=2x%2B13%3D22)
⇒![2x=22-13](https://tex.z-dn.net/?f=2x%3D22-13)
⇒![2x=9](https://tex.z-dn.net/?f=2x%3D9)
⇒![x=\frac{9}{2}](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B9%7D%7B2%7D)
⇒![x=4.5](https://tex.z-dn.net/?f=x%3D4.5)
Thus the cost of one CD is $4.5
Hence the combine cost of one DVD and CD = $6.5+ $4.5=$11