[求助]prep 上几道题

aj_goodnews

实在不好意思， 给大家添麻烦， 数学挺差的

198.
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If @ denotes one of the four arithmetic operations addition, subtraction, multiplication and division, what is the value of 1 @ 2 ?

 

(1) n @ 0 = n for all integers n.

 

(2) n @ n = 0 for all integers n.

答案是B 可是2 中若N是0 的话，岂不是加减乘除都可以？

113.
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In a certain year the United Nations' total expenditures were $1.6 billion.  Of this amount, 67.8 percent was paid by the6 highest-contributing countries, and the balance was paid by the remaining 153 countries.  Was Country X among the
            6 highest-contributing countries?

 

(1) 56 percent of the total expenditures was paid by the 4 highest-contributing countries, each of which paid more than Country X.

(2) Country X paid 4.8 percent of the total expenditures

这题什么意思啊

For any triangle T in the xy-coordinate plane, the center of T is defined to be the point whose x-coordinate is the average (arithmetic mean) of the x-coordinates of the vertices of T and whose y-coordinate is the average of the y-coordinates of the vertices of T.  If a certain triangle has vertices at the points (0,0) and (6,0) and center at the point (3,2), what are the coordinates of the remaining vertex?

 

(A) (3,4)

(B) (3,6)

(C) (4,9)

(D) (6,4)

(E) (9,6)

还是不明白意思

9.4  9.9  9.9  9.9  10.0  10.2  10.2  10.5

The mean and the standard deviation of the 8 numbers shown are 10.0 and 0.3, respectively.  What percent of the 8 numbers are within 1 standard deviation of the mean?

 

(A) 90%

(B) 85%

(C) 80%

(D) 75%

(E) 70%

这种standard deviation 题一直不会

Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it.  If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1)  The probability that the ball will both be white and have an even number painted on it is 0.

(2)      The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2

谢谢大家