两道数学题

09saiwinner

1、The arithmetic mean of a data set is 46 and the standard deviation of the set is 4. Which value is exactly 1.5 standard deviations from the arithmetic mean of the set?

A. 42  B.44.5  C.47.5  D. 50  E. 52

答案：E

请问这道题的问题到底是什么意思呢？怎么算？谢谢！

2、Jerome wrote each of the integers 1 through 20, inclusive, on a separate index card. He placed the cards in a box, then drew cards one at a time randomly from the box, without returning the cards he had already drawn to the box. In order to ensure that the sum of all the cards he drew was even, how many cards did Jerome have to draw?

A. 19  B. 12  C. 11  D. 10  E. 3

有哪位好心人可以帮忙翻译一下这道题目或者说一下大概意思。。。我实在有些不明白。。。

具体应该怎么算呢？ 万分感谢！！

09saiwinner

补充：第二题答案是B

shawntws

1、The arithmetic mean of a data set is 46 and the standard deviation of the set is 4. Which value is exactly 1.5 standard deviations from the arithmetic mean of the set?

这道题的意思应该是  哪一个数是恰好距离平均数1.5个standard deviation？

所以46+(1.5x4)=52  或46-(1.5X4)=40

A. 42  B.44.5  C.47.5  D. 50  E. 52

答案有52  选E

2、Jerome wrote each of the integers 1 through 20, inclusive, on a
separate index card. He placed the cards in a box, then drew cards one
at a time randomly from the box, without returning the cards he had
already drawn to the box. In order to ensure that the sum of all the cards he drew was even, how many cards did Jerome have to draw?

A. 19  B. 12  C. 11  D. 10  E. 3

这题的意思是，箱子里有写着1～20数字的卡片，抽出的卡片就不会在放回去了。如果要确定所有抽出的卡片的数字总和一定为偶数，那么要抽几张卡？

我们知道   odd+even = odd   （1）

                  even+even= even  （2）                        

                   odd+ odd = even  （3）

在后两种情形下，可能只要两张就可以了。但在第一种情形下，最糟的情况就是第一张抽到odd，但后面十张都抽到even，到第十二张时，因为只剩下odd，odd+odd= even，符合题目所要求

因此选答案(B)

希望有回答到你的问题

gyyygyyy

第一题：意思大概是，离平均值有1.5个方差的数值，即46±1.5*4=40or52

第二题：意思大概是，从盒子里抽出多少张排，肯定保证sum是偶数，

最坏的情况下，第一次抽奇数，接下来十次都是抽偶数，再抽一次奇数，一共得抽12次。

09saiwinner

恩~明白了！

谢谢shawn!

09saiwinner

谢谢gyyygyyy!!

好有效率！：）