A school decides to refill its cylindrical rooftop water tank, which has a radius of 3 metres and a height of 4 metres, using water from a rectangular underground rainwater harvesting pit measuring 6 metres in length, 5 metres in breadth, and 5 metres in depth. After filling the rooftop tank completely, what fraction of water remains in the underground reservoir?
(a) 1/2
(b) 1/3
(c) 1/4
(d) 1/5

Question

A school decides to refill its cylindrical rooftop water tank, which has a radius of 3 metres and a height of 4 metres, using water from a rectangular underground rainwater harvesting pit measuring 6 metres in length, 5 metres in breadth, and 5 metres in depth. After filling the rooftop tank completely, what fraction of water remains in the underground reservoir?
(a) 1/2
(b) 1/3
(c) 1/4
(d) 1/5

ONLiNE UPSC · Accepted Answer

Volume of rooftop tank (cylinder):
V = &pi;r2h = &pi; &times; 32 &times; 4 = 36&pi; m3 &asymp; 113.1 m3
Volume of underground reservoir (cuboid):
6 &times; 5 &times; 5 = 150&thinsp;m3
Water remaining:
150 &minus; 113.1 = 36.9 m3
Fraction remaining:
36.9/150 &asymp; &frac14;
Hence, option c is correct.

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M Question 1	⏱ 0
A school decides to refill its cylindrical rooftop water tank, which has a radius of 3 metres and a height of 4 metres, using water from a rectangular underground rainwater harvesting pit measuring 6 metres in length, 5 metres in breadth, and 5 metres in depth. After filling the rooftop tank completely, what fraction of water remains in the underground reservoir? (a) 1/2 (b) 1/3 (c) 1/4 (d) 1/5