(a) 18 and 35
Factors of 18 are 1, 2, 3, 6, 9 and 18
Factors of 35 are: 1, 5, 7 and 35
Since, 18 and 35 have no common factor except 1.
Thus, 18 and 35 are co-prime numbers.
(b) 15 and 37
Factors of 15 are: 1, 3, 5 and 15
Factors of 37 are: 1, 37
Since, 15 and 37 have no common factor except 1.
Thus, 15 and 37 are co-prime numbers.
(c) 30 and 415
Factors of 30 are: 1, 2, 3, 5, 6, 10, 15 and 30
Factors of 415 are: 1,5,83 and 415
Their common factors are: 1 and 5
Thus, 30 and 415 are not co-prime numbers.
(d) 17 and 69
Factors of 17 are: 1 and 17
Factors of 69 are: 1, 3, 23 and 69
Since, 17 and 69 have no common factor except 1.
Thus, 17 and 69 are co-prime numbers.
(e) 81 and 18
Factors of 81 are: 1, 3, 9, 27 and 81
Factors of 18 are: 1, 2, 3, 6, 9 and 18
Common factors of 81 and 18 are 3 and 9 other than 1.
Thus, 81 and 18 are not co-prime numbers.