For $1.80 a grocer buys a case of fruit which contains 12 dozen. She knows that tow dozen will spoil before she sells them. At what price per dozen must she sell the good ones to gain 1/3 of the whole cost?

Answer 1

(1/3) * $1.80 = $0.60. = Income.

P = $0.60 / (12-2) = $0.06 / doz.

Answer 2

GAIN (1/3) of the whole cost of $1.80, is (1.8+0.6) dollars. The cost given was for all 12 dozen. NOW, the selling cost, or the revenue must be 2.40 dollars. This 2.40 dollars must be equally distributed among the 10 dozen which are still good.
2.40 dollars per 10 dozen is:
2.40/10=0.24 dollars per dozen.
This is 24 cents per dozen.