1、(1)√
(2)×
(3)×
(4)√
(5)√
2、(1)B
(2)C
(3)C
(4)B
(5)A
3、(1)6,12,18,24,30,36
(2)无限 它本身
(3)20 5和4 4和5 20
(4)奇数有:11,13,15,17,19
偶数有:10,12,14,16,18,20
质数有:11,13,17,19
合数有:10,12,14,15,16,18,20
(5)2的倍数:18,90,130
5的倍数:75,90,130
3的倍数:18951,63,75,90,
2、3和5的倍数:90
(6)20
(7)6
4、13,26,39,52,65,78,91
5、(1)1,15,3,5
(2)1,24,2,32,3,8,4,6
(3)1,18,2,9,3,6
(4)1,20,2,10,4,5
6、(1)1,25,5
(2)25,50,75,100
(3)25
7、奇数有:1,35,37,9,11,25,21,23
偶数有:12,10,54,6,8
质数有:37,11,23
合数有:12,35,10,54,9,25,6,8,21
8、(1)2 0
(2)0
(3)1 0