JEE Main 2022 · 26 Jun · Shift 2, Mathematics question 26

If $\left({}^{40}C_0\right)+\left({}^{41}C_1\right)+\left({}^{42}C_2\right)+\dots+\left({}^{60}C_{20}\right)=\dfrac mn\,{}^{60}C_{20}$, $m$ and $n$ are coprime, then $m+n$ is equal to ______.