Question

Identify whether the given pair of numbers is co-prime or not: $3\mathrm{and}21$

Answer 1

Co-prime number: Two numbers are said to be co-prime or relatively prime if their HCF is $1$ or if they have no common factors other than $1$.

We have $3\mathrm{and}21$

$$\begin{gathered} 3=3\times 1 \\ 21=3\times 7 \end{gathered}$$

$3\mathrm{and}21$ have $3$as their common factor.

Hence, $3\mathrm{and}21$ are not co-prime.