几道新prep题求解

ronin3036

1.If p is a positive odd integer.What is the remainder when p is divided by 4?

(1)略(2)p is the sum of the squares of two positive integers.

（2）为什么能推出呀？

2.a@b代表a+b-ab           (a@b)@c=a@(b@c)为啥成立呀？

3.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,the p is?

a.2-10    b.10-20  c.20-30  d.30-40  d40以上

4.If x and y are integers greater than 1,is x a multiple of y?

(1)3y^2+7y=x       (2)x^2-xis a multiple of y

5.For eache of her sales,a saleswoman receives a commission equal to 20%of the first $500 of the total amount of the sale,plus30% of the total amount of the sale in excess of $500.If the total amount of one of her sales was $800,the sales woman's comission was qpproximately what precent of the total amount of the sale?这题主要是被一堆of弄迷糊了，谁能把of的逻辑捋下，不胜感激！！！

23就考了，大佬们帮帮忙解决下吧，谢谢！