Final answer:
To find out the number of brushes you have, divide the total cost of paint divided by the cost of one brush.
Step-by-step explanation:
To find out how many brushes you have, you can set up an equation using the given information. Let x represent the number of brushes. The cost of brushes is $0.5, so the equation would be 0.5x = $20. To find x, you would divide both sides of the equation by 0.5. Therefore, x = 40. So, if you use twice as many brushes, you would have 80 brushes.