GRE quant problem...

An electric meter is sold at a gain of 16%.if it were sold for 20$ more,there would have been a gain of 20%. find c.p ?

solution is:

cp is 500…

since adding $20 will make the %age increase of 4 % , it means 20 is 4 % of the cp… so u can find the cp…

1.16X + 20 = 1.20X
X = 20 / .04
X = 500