Consider an area of cross-section of pipe as shown in the figure.

Radius (r_{1}) of circular end of pipe = 20/200 = 0.1 m

Area of cross-section = π r_{1}^{2} = π x (0.1)^{2}

= 0.01π m^{2}

Speed of water = 3 km/h =3000/60 =50 meter/min

Volume of water that flows in 1 minute from pipe

= 50 × 0.01π = 0.5π m^{3}

Volume of water that flows in t minutes from pipe = t × 0.5π m^{3 }

^{}

Radius (r_{2}) of circular end of cylindrical tank =10/2 =5 m

Depth (h_{2}) of cylindrical tank = 2 m

Let the tank be filled completely in t minutes.

Volume of water filled in tank in t minutes is equal to the volume of water flowed in t minutes from the pipe.

Volume of water that flows in t minutes from pipe = Volume of water in tank

t × 0.5π = π ×(r_{2})^{2} ×h_{2}

t × 0.5 = 5^{2} ×2

t = 100

Therefore, the cylindrical tank will be filled in 100 minutes.