请教两道数学题目，请各位帮忙

jundai2003

一。If p and n are positive integers and p > n, what is the remainder when p2 - n2 is divided by 15 ?

(1) The remainder when p + n is divided by 5 is 1.

(2) The remainder when p - n is divided by 3 is 1.

答案为：E

二。If r and s are positive integers, is s/r an integer?

(1) Every factor of s is also a factor of r.

(2) Every prime factor of s is also a prime factor of r.

答案为：A

不知道解题思路

lookatme

For question 1: Use examples.

If p = 5, n = 1. (p+n) = 6, divided by 5 and remainder is 1.

                 p-n=4, divided by 3 is 1.

(p+n)(p-n) = 24, divided by 15 and remainder is 9.

If p = 9, n = 2. (p+n) = 11, divided by 5 and remaider is 1.

                 (p-n) = 7, divided by 3 and remaider is 1.

(p+n)(p-n) = 18, divided by 15 and remainder is 3

So answer is E.