Senior Mathematical Challenge 2011 Q22

$\frac{\tan10^{\circ}\tan20^{\circ}}{\tan50^{\circ}}$

$\frac{\tan10^{\circ}\tan20^{\circ}}{\tan70^{\circ}}$

$\frac{\tan10^{\circ}\tan50^{\circ}}{\tan70^{\circ}}$

$\frac{\tan20^{\circ}\tan50^{\circ}}{\tan70^{\circ}}$

$\frac{\tan10^{\circ}\tan70^{\circ}}{\tan50^{\circ}}$