Question

A DVD costs twice as much as a music CD. Jack buys 2 DVDs and 2 CDs and spends $45. Determine how much one CD costs, in dollars. [Only an alegbraic solution can receive full credit]

Answer 1

Let
`d=` the cost of a DVD
Let
`c=` the cost of a CD

We have

`d=2c`
and

`2d+2c=45`

We can replace
`d` with
`2c` in the second equation and get

`2(2c)+2c=45`

`\rightarrow 4c+2c=45`

`\rightarrow 6c=45`

`\rightarrow c=7.5\rightarrow\$7.50`