Re: The diameter and the height of a circular cylinder are 20 feet and 4 f
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08 Mar 2025, 04:47
As diameter is twice the radius, if the diameter of the base of the cylinder is 20 feet, its radius is 10 feet $\(=120\)$ inches ( $\(=r\)$ say ) ( 1 feet $\(=12\)$ inches ).
The level/height at which the cylinder to be filled is 3 feet 6 inches $\(=3 \times 12+6=36+6=42\)$ inches ( $\(=\mathrm{h}\)$ say).
Note: - Though the original height of the cylinder is 4 feet, but as the cylinder is to be filled up to 3 feet 6 inch height, the height while calculating the volume would be considered as 3 feet 6 inches only.
So, the volume of water in cylinder is $\(\pi \mathrm{r}^2 \mathrm{~h}=\frac{22}{7} \times(120)^2 \times 42=1900800\)$ cubic inches which is same as $\(\frac{1900800}{231}=\frac{57600}{7}\)$ gallon (Using 1 gallon $\(=231\)$ cubic inches)
Hence the answer is (B).