Question

Cathy sells twice as many pink sweaters as green sweaters each month. She averages 20 less green sweaters than pink sweaters each month. How many of each color sweater did Cathy sell?

Answer 1

Number of green sweaters = x
Number of pink sweaters = y = 2x

As per the question,

x = y - 20
=> x = 2x - 20
=> 20 = 2x - x
=> x = 20

So, x = 20, y = 40

Answer 2

p = 2g
g = p-20

now just solve for p and g.