Q8:

At a certain food stand, the price of each apple is ¢ 40 and the price of each orange is ¢ 60. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is ¢ 56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is ¢ 52?

A. 1

B. 2

C. 3

D. 4

E. 5

Why the key is E. I think it should be B.

(8-2)=6 (6x56-2x40)/(2+6)=52.

（560－60x）＝（10－X）52（X代表减少的数量）

X＝5。像这类题目，你自己多算一遍，就明白了。关键是细心。