请教问题，大家帮忙解答啊

1).Is the integer r divisible by 3?      A

   (1).r is the product of 4 consecutive positive integers.

   (2).r<25

第一个条件怎么算啊？

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

    (1).3y²+7y=x

    (2).x²-x is a multiple of y

3). If M is a finite set of negative integers, is the total number of integers in M an odd number?   B

    (1).the product of all the integers in M is odd

    (2).the product of all the integers in M is negative

4).Each person attending a fund-raising party for a certain club was charged the same admission fee. How many people attended the party?   C

    (1). if the admission fee had been $0.75 less and 100 more people had attended, the club would have received the same amount in admission fees.

    (2).if the admission fee had been $1.50 more and 100 fewer people had attended, the club would have received the same amount in admission fees.

怎么没人帮忙啊？拜托啊

1).Is the integer r divisible by 3?      A

   (1).r is the product of 4 consecutive positive integers.

   (2).r<25

假设n能被3整除，n+3, n+6....都能被3整除，这个数列的公差是3，所以连续4个整数肯定又能被3整除的数，选A

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

    (1).3y²+7y=x

    (2).x²-x is a multiple of y

(1)能推出 y(3y+7)=x 因为y是整数，所以x是y的倍数

(2)能推出y是x的倍数

所以选A

3). If M is a finite set of negative integers, is the total number of integers in M an odd number?   B

    (1).the product of all the integers in M is odd

    (2).the product of all the integers in M is negative

很明显 B  奇数个偶数的乘积是负的

4).Each person attending a fund-raising party for a certain club was charged the same admission fee. How many people attended the party?   C

    (1). if the admission fee had been $0.75 less and 100 more people had attended, the club would have received the same amount in admission fees.

    (2).if the admission fee had been $1.50 more and 100 fewer people had attended, the club would have received the same amount in admission fees.

由（1） (x-0.75)*(y+100)=xy

由（2） (x+1.5)*(y-100)=xy

联合两个条件可解，选C  (注：x为admission fee    y为人数)

建议去看一些基础的概念