A discount of 20 percent on an order of goods followed by a discount of 20 percent amounts to

A) the same as one 45 percent discount

B) the same as one 40 percent discount

C) the same as one 36 percent discount

D) the same as one 30 percent discount

E) the same as one 25 percent discount

The OA is the option C.

Why is C? Shouldn't it be B? Experts, can you explain this PS question to me? Thanks.