[求助]请教几道模考里的题

1、For every positive even integer n,the function h(n)is defined to be the product of all the even integers from 2 to n,inclusive.If p is the smallest prime factor of h(100)+1,then p is

A  from 2 to 10

B  from 10 to 20

C  from 20 to 30

D  from 30 to 40

E  above 40

答案是E  (解题思路是什么）

2、On Jane's credit card account,the average daily balance for a 30-day billing cycle is the average of the daily balances at the end of each of the 30 days.At the beginning of a certain 30-day billing cycle,Jane's credit card account had a balance of $600,Jane made a payment of $300 on the account during the billing cycle,if no other amounts were added to or subtracted from the account during the billing cycle.what was the average daily balace on Jane's account for the billling cycle.

(1)Jane's payment was credited on the 21st day of the billing cycle.

(2)The average daily balance through the 25th day of the billing cycle was $540.

答案是D（这道题的意思没看懂）

3、For which of the following function is f(a+b)=f(a)+f(b) for all positive numbers of  a and b?

A  f(x)=x^2

B   f(x)=x+1

C   f(x)=x^1/2

D   f(x)=2/x

E   f(x)=-3x

答案是E  （这类function的题都不太明白）

请指教！谢谢！

1. h(100)+1=2*4*6*8*……*98*100 而h(100)的smallest prime factor
应该是47，所以p=h(100)+1 the smallest prime factor一定>47，所以选E，记得思路应该是这样的

3. f(a+b)=f(a)+f(b)  比如A f(x)=x^2 则意味着如果你觉得(a+b)^2=a^2+b^2
那么就对了。你想想就知道了，选E

2.太晚了明天看

1、h(100)的least prime factor为什么不是2呢？sorry,我的这个问题可能很2，但是我想知道47是怎么算出来的，不是硬背的吧。。。

2、awaiting for you,thanks!