A potential difference of 220 V is maintained across a 12000 ohm rheostat AB . The voltmeter V has a resistance of 6000 ohm and point C is at one fourth of the distance from A to B. What is the reading in the voltmeter ?

Resistance of the wire between A and C is 
$\frac{12000}{4}=3000\mathrm{\Omega }$ 

This is in parallel to the voltmeter of resistance 6000Ω. Net resistance between A and C is
${\mathrm{R}}_{\mathrm{AC}}=\frac{3000\times 6000}{3000+6000}=2000\mathrm{\Omega }$
Voltmeter reading 
$={\mathrm{V}}_{\mathrm{AC}}=\frac{\left(220\right){\mathrm{R}}_{\mathrm{AC}}}{{\mathrm{R}}_{\mathrm{BC}}+{\mathrm{R}}_{\mathrm{CA}}}=\frac{220\times 2000}{9000+2000}=40\mathrm{V}$