SOLUTION: Kenny paid $120 for 4 cds and 3 dvds. Each dvd cost $12 more than a cd. what was the cost of three dvds?

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Question 769353: Kenny paid $120 for 4 cds and 3 dvds. Each dvd cost $12 more than a cd. what was the cost of three dvds?
Answer by Jc0110(165) About Me  (Show Source):
You can put this solution on YOUR website!
Let the cost of 1 CD to be x whereas the cost of 1 DVD to be y.
4x%2B3y=120 ---> Equation 1
y=x%2B12 ---> Equation 2 ... Substitute y=x%2B12 into Equation 1
4x%2B3%28x%2B12%29=120
4x%2B3x%2B36=120
4x%2B3x=120-36
7x=84
x=84%2F7
x=12 ... Substitute x=12 into Equation 1
4%2812%29%2B3y=120
48%2B3y=120
highlight%283y%29=120-48 ---> 3y is made as the subject of the equation because the cost of 1 DVD is y, thus the cost of 3 DVDs is 3y.
3y=72
Thus, the cost of 3 DVDs is $72.