Question

Which of the following are co-primes?

Options

• 91 and 72

• 34 and 51

• 21 and 36

• 15 and 20

Answer 1

The correct option is 91 and 72.
The H.C.F. of 72 and 91 is 1.
So, they are co-primes.

Option 34 and 51 is not correct because 34 and 51 have 17 as their H.C.F.
Option 21 and 36 is not correct because 21 and 56 have 3 as their H.C.F.
Option 15 and 20 is not correct because 15 and 20 have 5 as their H.C.F.