Answer:
Option D
Explanation:
Volume of water displayed by 1 man = $4m^{3}$
Volume of water displayed by 500 men =$4\times 500$
=$2000m^{3}$
Let xm be the rise in water level in the tank.
Therefore, Volume of water in the tank = $80\times 50\times xm^{3}$
$80\times 50\times x=2000$
x=$\frac{2000}{80\times 50}$
=$\frac{1}{2}m$
= 50 cm
