A system of three polarizers $P_1, P_2, P_3$ is set up such that the pass axis of $P 3$ is crossed with respect to that of $P_1$. The pass axis of $P_2$ is inclined at $60^{\circ} \mathrm{C}$ to the pass axis of $P_3$. When a beam of unpolarized light of intensity 10 is incident on $P_1$, the intensity of light transmitted by the three polarizers is $I$. The ratio $\left(I_0 / I\right)$ equals (nearly):