急问几道PREP数学，12月3号要考了，请大家帮帮忙。先多谢了。

托福小小

1。A committee of three people is to be chosen from four married couples.  What is the number of different committees that can be chosen if two people who are married to each other cannot both serve on the committee?
(A)  16 (B)  24 (C)  26 (D)  30 (E)  32    ANS：E

2。If x is a negative integer, which of the following expressions has the LEAST value?
(A) x2 - 0.50 (B) x2 - 0.51 (C) x3 - 0.502 (D) x3 - 0.511 (E) x4 - 0.512
ANS：D。 我选了E，怎么看都是D，怀疑题目有问题。

3。In the arithmetic sequence t1, t2, t3, . . . , tn, . . . , t1 = 23 and tn = tn - 1 - 3 for each n > 1.  What is the value of n when tn = -4 ?
(A) - 1 (B) 7 (C) 10 (D) 14 (E) 20
ANS：C 没看懂那个“tn = tn - 1 - 3”是什么意思

4。A certain office supply store stocks 2 sizes of self-stick notepads, each in 4 colors:  blue, green, yellow, or pink.  The store packs the notepads in packages that contain either 3 notepads of the same size and the same color or 3 notepads of the same size and of 3 different colors.  If the order in which the colors are packed is not considered, how many different packages of the types described above are possible?
(A)  6 (B)  8 (C)  16 (D)  24 (E)  32
ANS：C 我选了B，觉得只有同SIZE，不同颜色的要考虑，两种不同SIZE的相加。

5。A vending machine is designed to dispense 8 ounces of coffee into a cup.  After a test that recorded the number of ounces of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts, in ounces, were selected from the data.  If the 1,000 recorded amounts have a mean of 8.1 ounces and a standard deviation of 0.3 ounce, how many of the 12 listed amounts are within 1.5 standard deviations of the mean?
(A) Four (B) Six (C) Nine (D) Ten (E) Eleven
ANS：E， 我选D，思路不决定对，觉得是[8.1+(0.3*1.5)] - [8.1- (0.3*1.5)] =0.9之间可以有多少个。

6。If d is the standard deviation of x, y, and z, what is the standard deviation of x + 5, y + 5, and z + 5 ?
(A) d (B) 3d(C) 15d (D) d + 5 (E) d + 15
ANS：A。我对这类方差的题很不懂。

7。During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?
 (1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.
ANS：A  我选了C，完全看不懂。

8。If p and n are positive integers and p > n, what is the remainder when p2 - n2 is divided by 15 ?
(1) The remainder when p + n is divided by 5 is 1.
(2) The remainder when p - n is divided by 3 is 1.
ANS：E。我选了C，没思路。

最后一题
9。Beth's bank charges a service fee on a regular checking account for each month in which the balance on the account falls below $100 at any time during the month. Did the bank charge a service fee on Beth's regular checking account last month?
(1) During last month, a total of $1,000 was withdrawn from Beth's regular checking account.
(2) At the beginning of last month, Beth's regular checking account balance was $500.
ANS：E。 我选了C，应该是接近了，我不知道漏了题中的哪个条件。

各位能解多少是多少，非常感谢大家的帮忙。