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

Answer 1

V=2c, and 2v + 2c =45 you can substitute v for 2c in the second equation because they equal to get 4c +2c =45 6c =45 c = 45/6, so the answer is $7.50

Answer 2

$dvd=d \\ cd=c \\ \\ \left \{ {{d=2c} \atop {2d+2c=45}} \right. \\ \\ 2(2c)+2c=45 \\ 4c+2c=45 \\ 6c=45 \\ c=7.5 \\ \\ d=2(7.5) \\ d=15$

One CD costs $7.50.
One DVD costs $15.00.