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प्रश्न
A swimming pool is 20 m long 15 m wide and 3 m deep. Find the cost of repairing the floor and wall at the rate of Rs 25 per square metre.
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उत्तर
\[\text { Length of the swimming pool = 20 m }\]
\[\text { Breadth = 15 m}\]
\[\text { Height = 3 m }\]
\[\text { Now, surface area of the floor and all four walls of the pool = (length } \times \text { breadth) } + 2 \times \text { (breadth } \times \text { height + length } \times\text { height) }\]
\[ = (20 \times 15) + 2 \times (15 \times 3 + 20 \times 3)\]
\[ = 300 + 2 \times (45 + 60)\]
\[ = 300 + 210\]
\[ = 510 m^2 \]
\[\text { The cost of repairing the floor and the walls is Rs } 25 m^2 . \]
\[ \therefore\text { The total cost of repairing 510 m^2 area = 510} \times 25 = \text { Rs } 12750\]
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