一道不懂得ＧＷＤ３０数学题 ···

卡卡樱花猫

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


我算了　···之前５６的时候苹果是２个，橘子８个，５２的时候苹果４个橘子６个　···答案为什么是Ｅ　·····不理解～～

卡卡樱花猫

$10,000 is deposited in a certain account that pays r percent annual interest compounded annually, the amount D(t), in dollars, that the deposit will grow to in t years is given by D(t) = 10,000 {1+(r/100)}^t.What amount will the deposit grow to in 3 years?
(1)D(t) = 11,000
(2) r =10
为什么答案是Ｃ？？明明只要有了第二个就可以算出来了啊？？

(1)D(t) = 11,000
(2) r =10
为什么答案是Ｃ？？明明只要有了第二个就可以算出来了啊？？

charmix

答案给错了？我算好像也是B

arleneyau

...52的时候apple 2个，orange 3个啊。。（2*40+3*60）/5=52...楼主和楼上是不是看错题了？How many oranges must Mary put back ，橘子要拿掉哦

哈哈王

1) 52*(10-放回去的个数）需要是整数，因此只有5个能使之成立。 也就是说52*5=260元 （2个苹果三个橙子）

arleneyau

第二题你是不是写错答案了？我觉得也不应该是C，然后论坛搜了下都说答案给的是D，争议在（1）条件。。这个公式说明它是常值，所以也可以用。。

charmix

我还以为一定divide by10呢

卡卡樱花猫

懂了！！！