Magnetism And Matter

A magnet having a magnetic dipole moment ' M is placed in two magnetic fields ' $\mathrm{B}_1$ ' and ' $\mathrm{B}_2$ ' respectively. If it is displaced slightly from the equilibrium position, it oscillates 60 times in 20 second in field ' $\mathrm{B}_1$ ' and 60 times in 30 second in field ' $B_2$ '. The ratio of field ' $B_1$ ' to that of ' $\mathrm{B}_2{ }^{\prime}$ is