向CD同志们请求帮助~谢谢!

on a purchase of $120, a store offered a payment plan consisting of a $20 down payment and 12 monthly payments of $10 each. What percent of the purchase price, to the nearest tenth of a percent, did the customer pay in interest by using this plan?

a 16.7%

b 30

c 75.8

d 106.7

谢谢各位战友啦!!!

答案是A, 我就没读明白~~

是说interest是purchase price的percentage：20/120=A

谢谢哈~~