Which of the following numbers are co-prime? $( a).\ 18$ and $35$ $( b).\ 15$ and $37$.

Given: $( a).\ 18\ and\ 35\ \ \ ( b).\ 15\ and\ 37$.

To do: To find the co-prime numbers.

A set of numbers or integers which have only $1$ as their common factor is called co-prime number.

$( a)\ 18$ and $35$.

Factors of $181,\ 2,\ 3,\ 6,\ 9,\ 18$

Factors of $35=1,\ 5,\ 7,\ 35$

Common factor of $18$ and $35=1$

Here both have only $1$ as a common factor, therefore, $18$ and $35$ are co-prime numbers.

$( b).\ 15$ and $37$.

Factors of $15=1,\ 3,\ 5,\ 15$

Factors of $37=1,\ 37$

Common factor of $15$ and $37=1$

Here both have only $1$ as a common factor, therefore, $15$ and $37$ are co-prime numbers.