Question

Which of the following is a pair of co-primes?

• A. $(14,35)$
• B. $(18,25)$
• C. $(31,93)$
• D. $(32,62)$

Answer 1

The correct option is B $(18,25)$

If the H.C.F of two numbers are $1$ they are said to be co-prime

Factors of $14=1,2,7$

Factors of $35=1,5,7$

$\Rightarrow$ Common factor $=1,7$

$\therefore$ $(14,35)$ is not pair of co-prime.

Factors of $18=1,2,3,6,9$

Factors of $25=1,5$

$\Rightarrow$ Common factor $=1$

$\therefore$ $(18,25)$ is pair of co-prime.

Factors of $31=1,31$

Factors of $93=1,3,31$

$\Rightarrow$ Common factor $=1,31$

$\therefore$ $(31,93)$ is not pair of co-prime.

Factors of $32=1,2,4,8,16$

Factors of $62=1,2,31$

$\Rightarrow$ Common factor $=1,2$

$\therefore$ $(32,62)$ is not pair of co-prime.