请教4道数学，比较难我觉得！

lijiaxuan810823

1.At a garage sale, all of the prices of the items sold were different.  If the price of a radio sold at the garage sale was both the 15th highest price and the 20th lowest price among the prices of the items sold, how many items were sold at the garage sale?

 

A.     33

B.     34

C.     35

D.     36

E.      37

ans is b，but i can not get the means of the question

2At a certain company, each employee has a salary grade s that is at least 1 and at most 5.  Each employee receives an hourly wage p, in dollars, determined by the formula p = 9.50 + 0.25(s – 1).  An employee with a salary grade of 5 receives how many more dollars per hour than an employee with a salary grade of 1?

 

A.     $0.50

B.     $1.00

C.     $1.25

D.     $1.50

E.      $1.75

ans is c,but i chose b and sespected the ans.

3If an integer n is to be chosen at random from the integers 1 to 96, inclusive, what is the probability that n(n + 1)(n + 2) will be divisible by 8?

 

ans is 5/8, who can tell me the  method? i can suppose the ans approximately.

4

A box contains 10 light bulbs, fewer than half of which are defective.  Two bulbs are to be drawn simultaneously from the box.  If n of the bulbs in box are defective, what is the value of n?

(1)   The probability that the two bulbs to be drawn will be defective is 1/15.

(2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.

                  

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.

thank you very much !

 

gyyygyyy

第一题：收音机的价格第15贵，第20便宜，那有多少件商品，当然就是15+20-1=34了。

第二题我也选B，不知答案有没有错，待解？

第三题：n是偶数的话，都可以满足条件，所以n=2,4,6,……,96，共48个；

n+1是8的倍数也满足条件，则n=8-1,16-1,……,96-1，共12个；

所以概率是(48+12)/96=5/8

第四题：是不是选D？

根据第一个条件，Cn,2 / C10,2 = 1/15, 得n=3；

根据第二个条件，Cn,1 * C(10-n),1 / C10,2 = 7 / 15, 得n=3（fewer than half are defective）

lijiaxuan810823

多谢，多谢，第四题是d，我发现还是对题意理解不够，呵呵