[UPSC CSE 2010] Angular momentum, spin etc (Q321, 10M)

The normalized wave function for the electron in hydrogen atom for the ground state is \psi(r)=(\pi a_0^3)^{-1/2}\exp\left(-\frac{r}{a_0}\right) Where a_0 is the radius of the first Bohr orbit. Show that the most probable position of the electron is a_0.