A swimming pool 70 m long, 44 m wide and 3 m deep, is filled by water issuing from a pipe of diameter 35 cm, at 6 m per second. How many hours does it take to fill the pool?

Volume of the swimming pool = 70 × 44 × 3 = 9240 m³

Radius of the pipe = $\dfrac{\text{Diameter}}{2} = \dfrac{35}{2} \times \dfrac{1}{100} = \dfrac{35}{200} = 0.175$ m

Volume of water flowing out of the pipe per second = Area of cross section of the pipe × rate of flow of water

= πr² × 6 m/s

$= \dfrac{22}{7} \times (0.175)^2 \times 6 \\[1em] = \dfrac{22}{7} \times 0.030625 \times 6 \\[1em] = \dfrac{4.0425}{7} \\[1em] = 0.5775 \text{ m}^3$

Required time = $\dfrac{\text{Volume of swimming pool}}{\text{volume of water flow per second}}$

$= \dfrac{9240}{0.5775} \\[1em] = 16000 \text{ seconds} \\[1em] = \dfrac{16000}{60 \times 60} \\[1em] = \dfrac{40}{9} \\[1em] = 4\dfrac{4}{9} \text{ hours.}$

Hence, time required to fill the pool is $4\dfrac{4}{9}$ hours.