一道不懂得ＧＷＤ３０数学题 ···

ballackahn

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～～

ballackahn

ＧＷＤ３０数学中的一道～～～求解答
$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？？

torresAing

答案给错了？我算好像也是B

vespertine612

...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

laughaholiker

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）

vespertine612

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。。

torresAing

我还以为一定divide by10呢

ballackahn

懂了！！！ 谢谢