[問題] GWD13-8

由 **kwtluck** » 2006-09-10 01:41

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

The answer is E

令apple=A , orange=B
A+B=10---------[1]
40A+60B=560----[2] [1and2]聯立得:A=2,B=8
40A+60B=520----[3] [1and3]聯立得:A=4,B=6

答案不是應該要退回2個橘子?
請教各位大大 ;-$

Thanks!~~

由 **FrankChang** » 2006-09-10 16:19

妳的式子列到第二行都對,
不過新的式子列錯了,保持蘋果數量減少橘子數量,假設新的橘子數量B',
40*2+60*B'=52(2+B'),
B'=3,退給老闆5顆

由 **kwtluck** » 2006-09-11 16:17

FrankChang \$m[1]:妳的式子列到第二行都對,
不過新的式子列錯了,保持蘋果數量減少橘子數量,假設新的橘子數量B',
40*2+60*B'=52(2+B'),
B'=3,退給老闆5顆

謝謝FrankChang大大 ;yes;

你也是這個月的考生嗎?
大家一起加油囉!! ;))

[問題] GWD13-8

[問題] GWD13-8

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