快考试了，问GWD－4两道数学

On Saturday morning, Malachi will begin a camping vacation and he will
return home at the end of the first day on which it rains.  If on the
first three days of the vacation the probability of rain on each day is 0.2,
what is the probability that Malachi will return home at the end of the day on
the following Monday?

A.     0.008

B.     0.128

C.     0.488

D.     0.512

E.      0.640

If n is a positive integer and r
is the remainder when (n – 1)(n + 1) is divided by 24, what is
the value of r?

(1)     2 is
not a factor of n.

(2)     3 is
not a factor of n.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH
statements TOGETHER are
sufficient, but NEITHER
statement ALONE is sufficient.

D. EACH
statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

对于x is  a factor of y，这种类型的题总是不明白是什么意思，这X是y的因子是什么意思也不知道其真正含义，数学忘的多，请大家帮忙

谢谢

先说第一个哈～

意思大体这样：这个人周六要出去野炊，但是如果碰到下雨的情况的话，就要在下雨这天返回（at the end of the first day on which it rains）也就是说
                如果周六下雨，那么周六晚上就得回来，不能等到周日或以后，周六到周一
                每天下雨的概率都是0.2，问他周一返回的概率，也就是说周一下雨了呗，而且前几天都没下雨

解法
                     由于每天是否下雨
                都是相互独立事件
                那么周一返回的概率=0.8×0.8×0.2=0.128

对否？

昨天忘记回复第二题啦

这个题我算了半天 选了E也不知道对不对

至于因子问题 如果x能被y整除 那么就说y是x的因子了，当然x,y得是整数（非官方定义...但大体就是这么个意思吧）

比如说 24 ，因子就有很多 1，2，3，4，6，8，12，24  因为这些数都能被24整除 

而你把24因数分解后 发现质因子只有2和3

I think the answer to the second question is C  

24=3*(2^3)

Since 2 or 3 are not the factor of n, (n-1)*(n+1)must contains the factors of both 2, 2^2 and 3.