Question

Which of the following numbers are co-prime?
a) 18 and 35
b) 15 and 37
c) 30 and 415
d) 17 and 68
e) 216 and 215
f) 81 and 16​

Answer 1

Co-prime are numbers that do not share any common factors except 1

Question (a);

Prime factors of 18 = 2 x 3²

Prime factors of 35 = 5 x 7

HCF = 1

Answer: Yes, they are co-prime

Question (b);

Prime factors of 15 = 3 x 5

Prime factors of 37 = 37

HCF = 1

Answer: Yes, they are co-prime

Question (c);

Prime factors of 30 = 2 x 3 x 5

Prime factors of 415 = 5 x 83

HCF = 5

Answer: No, they are not co-prime

Question (d);

Prime factors of 17 = 17

Prime factors of 68 = 2² x 17

HCF = 17

Answer: No, they are not co-prime

Question (e);

Prime factors of 216 = 2³ x 3³

Prime factors of 215 = 5 x 43

HCF = 1

Answer: Yes, they are co-prime

Question (f);

Prime factors of 81 = 3⁴

Prime factors of 16 = 2⁴

HCF = 1

Answer: Yes, they are co-prime