请教高手MATH 219

yzlinlin

219PS:two prime integars, the difference between them is 2, Ask: which of the following numbers could be the average of the two prime integars.
A. 11 B.21. C 26. D. 30 E.52
作者答案及思路：
DZ评价意见：difference between them is 2 =>应该是偶数，两别的两个数是偶数+-1
，其中30两边29,31为质数；E左边的51=3*17，排除。

我觉得21也可以啊，如19&23。

xiaogh

219PS:two prime integars, the difference between them is 2, Ask: which of the following numbers could be the average of the two prime integars.
A. 11 B.21. C 26. D. 30 E.52

[此贴子已经被作者于2003-12-21 8:00:32编辑过]

dz

the difference between them is 2，them指代two prime intergers.

数学请大家注意代词指代！

yzlinlin

以下是引用xiaogh在2003-12-21 8:00:00的发言：
219PS:two prime integars, the difference between them is 2, Ask: which of the following numbers could be the average of the two prime integars.
A. 11 B.21. C 26. D. 30 E.52

[此贴子已经被作者于2003-12-21 8:00:32编辑过]

从小学开始就犯3+4=9的错误，什么时候才能考虑周全呢？！

wuxinxinperfect

好可爱啊。哈哈

candy123

这道题究竟选什么啊？

wanze

d.30         31-29=2         ( 31+29)/2=30

Yuwusheng

看来不光我一人计算粗心。

donna

以下是引用Yuwusheng在2003-12-22 12:06:00的发言：
看来不光我一人计算粗心。

是啊！粗心是我们考G数学部分最大的天敌，我们一定要克服！