If a 10 percent deposit that has been paid toward the purchase of a certain product is $80, how much more remains to be paid? Choices:
A) $ 640
B) $ 680
C) $ 720
D) $ 760
E) $ 800

Rationale: "90 % remains to be paid so the remaining amount is 9 * 80 = $ 720 . the answer is c ."
Answer: C