Question

Tim will buy twice as many CD's as Raul.

Answer 1

Let
$x$
represent the number of CDs Raul will buy.

Then Tim will buy , 2 times of it. That is,
$2x$

Since Tim will be waiting for Raul to buy before he doubles it, Raul has become the independent variable and Tim the dependent variable.

We can write the equation in function notation as,

$T(R)=2R$

Or

$f(x)=2x$