Question

Which of the following numbers are co-prime?
(a) 24, 42
(b) 15, 36
(c) 11, 15

Answer 1

For two numbers to be coprime, they should have no common factor that divides both the numbers, except 1.
Checking for each option:

Case - a: 24, 42
The factors of 24 are 1, 2, 3, 4, 6, 8 and 12
The factors of 42 are 1, 2,3, 6, 7, 14 and 21

24 and 42 have common factors 2, 3 and 6 except 1, Hence
24 and 42 are Non-co-prime numbers.

Similarly,
Case - b: 15, 36
The factors of 15 are 1, 3, and 5
The factors of 36 are 1, 3, 4, 6, 9 and 18

Numbers have common factors except 1, Hence Non-co-prime numbers.

Similarly,
Case - c: 11, 15
The factors of 11 are 1 and 11
The factors of 15 are 1, 3 and 5

11 and 15 have no common factor except 1, Hence 11 and 15 are co-prime numbers.

∴ Pair of (11, 15) are the co-prime numbers.