几道prep数学，请教哈

ltwy16323

152.
                15540-!-item-!-187;#058&010751

A certain jar contains only b black marbles, w white marbles, and r red marbles.  If one marble is to be chosen at random from the jar, is the probability that the marble chosen will be red greater than the probability that the marble chosen will be white?

 

（1） r/(b+w)>w/(b+r)

 

(2)   b - w>r

A

 

29.   3873-!-item-!-187;#058&003594

If n denotes a number to the left of 0 on the number line such that the square of n is less than  1/100, then the reciprocal of n must be

 

(A) less than -10

(B) between -1 and 

(C) between   and 0

(D) between 0 and 

(E) greater than 10

这个题中reciprocal 是什么意思啊？

A

 

2.    140-!-item-!-187;#058&000076

If k is a positive integer, is k the square of an integer?

 

(1) k is divisible by 4.

 

(2) k is divisible by exactly four different prime numbers.

E

 

151.
                    15486-!-item-!-187;#058&010743

Is the average (arithmetic mean) of 5 different positive integers at least 30 ?

 

(1)  Each of the integers is a multiple of 10.

 

(2)  The sum of the 5 integers is 160.

D

 

 

题目有点多，还是希望大家给解答一下哈，谢谢了

 

 

genebaobao

152. 充要条件为r>w,而(1)可以推出r>W,如果r<=W，则(1)不成立

29:倒数

ltwy16323

谢谢哈，明白了

ltwy16323

又没有人再帮我打一下其他两道呢