Question

find rational number between 2 and 1

Answer 1

There are infinitely many rational numbers between any two integers. A simple way to get one of these rational numbers is to take average of the two integers :
$\dfrac{2+1}{2}~=~\dfrac{3}{2}$

$\dfrac{3}{2}$ lies exactly halfway between $2$ and $1$.

Answer 2

2+1 divided by =3 by 2