MATH PREP 模考题！！！求解！！！各位大侠帮帮忙！！！

airsty

1. if n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

(1) n+1 is divisible by 3
(2) n>20


答案：A
余数的题怎么入手？这考得机率非常高啊！！


2. Forwhich of the following functions is f(a + b) = f(a) + f(b) for all positivenumbers a and b ?

(A) f(x) = x 2
(B) f(x) = x + 1
(C) f(x) = √x
(D) f(x) = 2/x
(E) f(x) = -3x
答案：E
求思路！！！！！


3. To furnish a room in a model home, an interior decorator isto select 2 chairs and 2 tables from a collection of chairs and tables in awarehouse that are all different from each other.  If there are 5 chairs in the warehouse and if150 different combinations are possible, how many tables are in the warehouse?

(A) 6
(B) 8
(C) 10
(D) 15
(E) 30


答案：A


4. Six countries sent total 75 representatives, no two countries sent the same number. A country send the second greatest number, did country A send at least 10 representatives?
（1）one of the six countries sent 41 representatives
(2) country A send fewer thatn 12


答案是E
可觉得1是成立的啊，派41个的国家是派的最多的，A是第二如果不大于等于10，比如说是9， 其他4个国家最大只能派8，7，6，5 这加起来小于75啊
说明派送第二多的A 一定要大于10啊？？？这么想不对嘛？？？


5. when a certain tree was first planted, it was 4 feet tall. the height of the tree increased by a constant amount each year for the next 6 year. at the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year. how many feet did the height of the tree increased each year?
答：2/3


求帮忙解答下吧，哪儿道题都成！！！！！！！！！！！
眼看就考试啦！！！！这么简单得都不会啊。。。。。。。。。。


求救命啊！！！！跪谢跪谢！！！


另，数学有讨论群不？求加入组织啊！！！！！！！！！

alei415

第一题， (1) 4+7N=7(n+1)-3可以被3整除，所以余数R=0，充分；(2)随便找俩个数，21、22代进去算一下，余数不一样，不充分

第二题 ，把没个函数都带进去算一下就知道啦，E，f(a+b)=-3(a+b)=(-3a)+(-3b)=f(a)+f(b)

第三题 假设有X个桌子，可能的组合就是5*4/2*x*(x-1)/2=150，解方程，X=6

第四题 哎你怎么算的，41+9+8+7+6+5=76

第五题，假设每年长x, 第六年底是4+6x， 第四年底是4+4x, 所以2x/(4+4x)=1/5,解方程得x=2/3