A tank is 7 metre long and 4 meter wide wide. At what speed should water run through a pipe 5 cm broad and 4 cm deep so that in 6 hours and 18 minutes water level in the tank rises by 4.5 meter?

Answer: Option A

Rate of flow of water = x cm/minute
∴ Volume of water that flowed in the in 1 minutes
= (5 × 4 × x) = 20 x cu.cm.
∴ Volume of water that flowed in the tank in 6 hours 18 minutes.
i.e. (6 × 60 + 18) = 378 minutes
= 2x × 378 cu. cm.
According to question,
$$\begin{array}{rl}& \text{20}x\times 378=700\times 400\times 450\\ & \Rightarrow x=\left(\frac{700\times 400\times 450}{20\times 378}\right)\text{cm /minutes}\\ & \Rightarrow x=\left(\frac{700\times 400\times 450\times 60}{100000\times 20\times 378}\right)\text{km/hours}\\ & \Rightarrow x\text{ = 10 km/hours}\end{array}$$