235. n persons is surveyed about looking A newsletters and B newsletters. the number of seeing a is x% and the number of seeing B is y%, the number of seeing both A and B is z%,. ask:what is the number of not seeing A and not seeing B?(n,x,y,z is told. I don't remember clearly)
参考答案： n*(1-x%-y%+z%)
思路：

236. in the following equations, which has exactly one point that has the whole number of both x-coordinate and y-coordinate?
D. Y=X+1/2
E.Y=(the square root 3 )*x
参考答案：e
思路：与x,y轴平行或过原点

237. completing an order, machineA need x hours solely, machineB need y hours solely. ask: if machineA and machineB
work together, how many hours comleting 1/2 of this order?(x,y are told)
参考答案：(1/2)/[1/x+1/y]
思路：

238. A motorist travel from X to Z. Y is one point douring this trip(from X to Y). The average speed from X to Y is 15 miles per second. ask: what is the average speed from Yto Z?
(1). the average speed from X to Y is 10 miles per second
(2). the tome from Y to Z is 20 seconds.
参考答案：e
思路：确认老机井当中一点任意，而非中点

239. (n-1)(n+1)除以24的余数为R，求R
1）N可以被2整除
2）N可以被3整除
参考答案：E
思路：

240. 一个标准差的范围占68％，2个标准差占95％，问平均值为60，标准差10，求70到80之间的人数占总人数的比例，答案不记得，有个是14％，
参考答案：95%/2-68%/2=13.5%
思路：

242. What is the tenths digit of number n?
1) n > 0.2
2) 0 < n < 1
参考答案：e
思路：

243. one person makes a order on clothes. The shiping fee for the order is $3.95. Each of the cloth is $29.95. Ask how many clothes the person bought?
1) the total money spent on the order is [$280, $310]
2) the total money is [$300, $335]
参考答案：d
思路：注意什么价格

244. x-2, x-3, 1.5, X. X+1.5, If the median is 1, what is the X.
A.0
B.1
C.-1
D.-2
E.1.5
参考答案：b
思路：

245. x>y ?
(1) 2^x>3^y
(2) 5^x>4^y
I'm not sure if there are some other conditions. At least 2 or 3 thid DS questions about comparison.
参考答案：c
思路：考虑负数。

246. 4 teams debate to other 6teams. one team can debate at most once, the order is irrelevant, total detates between these teams
参考答案：24
思路：

247. 100 people, 48, 45 and 57 read book a,b,c, 20 people read both of three, 10 people read nothing, what is the number of the people only read two books.
A.20
B.30
C.40
D.50
E.70
参考答案：a
思路：作者答案c，老jj有此题，定论是20

248. a rectangular solid, Height:length:width is 3:2:2, the volume is X, what is the length expressed by x.
参考答案：(2x/3)^(1/3)
思路：

250. a hundred digit number, if each number is a prime number and the product of the three number is 144, what is the tens number of the least small hundred digit number.
参考答案：8
思路：2*8*9=144（注题目所称prime number似乎有误）