Q122
ArithmeticGeometry & Mensuration
A cylindrical cistern of diameter 25 cm is full of water. If 11 litres of water is drawn off, the water level in the cistern will drop by (Use $\pi = \frac{22}{7}$):
- a.$10\frac{1}{2}$ cm
- b.$12\frac{6}{7}$ cm
- c.$22\frac{2}{5}$ cm
- d.$20\frac{2}{5}$ cm
Answer: (C) $22\frac{2}{5}$ cm
11 litres = 11000 cm³ and the base area is $\frac{22}{7} \times 12.5^2 = \frac{6875}{14}$ cm². The drop is $11000 \times \frac{14}{6875} = 22.4$ cm = $22\frac{2}{5}$ cm. Using the diameter instead of the radius would give a much smaller drop.