On an order of 5 dozen boxes of a consumer product, a retailer receives an extra dozen free. This is equivalent to allowing him a discount of:________?

A. 15%
B. 16 1/6%
C. 16 2/3%
D. 20%

Explanation:

Clearly, the retailer gets 1 dozen out of 6 dozens free.

Equivalent discount = 1/6 * 100 = 16 2/3%.