Let x be the number of tubes of paint purchased. With this representation, the number of paintbrushes purchased is equal to 2x. The equation that would allow us to relate these variables with the given total amount is,
(4)(x) + (0.50)(2x) = 20
The value of x is equal to 4. Thus, 2x is equal to 8.
Answer: brushes = 8
paint = 4