A shopkeeper sold an article at $100 with 20% profit. Then find its cost price? Choices:  A) $ 120  B) $ 100  C) $ 91  D) $ 83  E) $ 69

Rationale: "cost price = selling price * 100 / ( 100 + profit ) c . p . = 100 * 100 / 120 = $ 83 ( approximately ) answer is d"
Answer: D