请教GWD第三套里面的几道数学题

狮子珊

我想请教大家GWD第三套里面的几道数学题~ 谢谢亲们啦~~~
14.How many seconds will it take for a car that is traveling at a constant rate of 45miles per hour to travel  a distance of 22 yards?(1mile=1,160)
答案：C.10

16.If n is a positive integer and r is the remainder when (n-1)(n+1)is divided by 24,what is the value of r?
(1).2 is not a factor of n
(2).3 is not a factor of n
答案：C

18.Last year the price per share of Stock  X increased by k percent and the earnings per share of Stock X increased by m percent ,where k is greater than m.By what percent did the ratio of price per share to earnings per share incease,in terms of k and m?
答案：D.(100(k-m))/(100+m)%

A certain roller coaster has 3 cars,and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster.If a certain passenger is to ride the roller coaster 3 times,what is the probability that the passenger will ride in each of the 3 cars?
答案.C.2/9

谢谢你们~~~~

狮子珊

谁可以救救我啊~~~~~

格格1113

16 【思路】 =
       (1) n = 3 , 5 , 7 ,9…… ,則r=8 , 1 ……,不充份
     (2)n=1 , 2 , 4,….,r=2 ,3………,不充份

(1) + (2) 不能被2 , 3整除 ,2 ,3 為 24 的公因數 ,所以n排除為24因數後,r=01) n not divisible by 2=> n is odd=> (n-1) and (n+1) must be consective even numbers.

if n=1, 0*2/24 leaves remainder 0
if n=3, 2*4/24 leaves remainder 8
not sufficient


2) n not divisible by 3=> n can be even or 1, 5, 7, 11, 13....

if n=5, 4*6/24 leaves remainder 0
if n=2, 1*3/24 leaves remainder 3
not sufficient

together,
n must be odd and not divisible by 3=> n can be 1, 5, 7, 11, 13...
if n=7, 6*8/24 leaves remainder 0
if n=11, 10*12/24 leaves remainder 0

hence C.