还有一道GMAT数学题At a certain food stand, theprice of each apple is _英语解答

还有一道GMAT数学题
At a certain food stand, theprice of each apple is ¢ 40 and the price of each orange is ¢60.Mary selects a total of 10 applesand oranges from the food stand, and the average (arithmetic mean) price of the10 pieces of fruit is ¢ 56.Howmany oranges must Mary put back so that the average price of the pieces offruit that she keeps is ¢ 52?

A.1
B.2
C.3
D.4
E.5
（为什么不选d,4个orange,6个apple,平均价格刚好是52呀）

人气：458 ℃　时间：2020-09-10 14:53:08

解答

Mary paid = 10(56) = ¢560
if the average price drop to ¢52,she paid =52x10 =¢520
She paid less = 560-520 =¢40
The price difference between orange and apple =60-40 = ¢20
so she must put back =40/20 = 2 pieces of orange
ans :B给的答案是E。。。。Mary paid = 10(56) = ¢560 = 8 oranges + 2 apples

let x be the number of oranges that Mary should put back

[(8-x)60 + 2(40)] /(10-x)=52
480x -60x +80 =520-52x
8x = 40
x=5
Ans: E