Discussion
A plot has a concrete path within its borders on all sides having uniform width of 4m. The plot is rectangular with sides 20m and 15m. Charge of removing concrete is Rs. 6 per sq.m. How much is spent in removing all the concrete?
Answer: B
The path lies within the plot's borders, so it eats 4 m in from each side and the untouched middle shrinks by 8 m in both directions.
\[ A_{\text{plot}} = 20 \times 15 = 300 \text{ m}^{2} \]
\[ A_{\text{inner}} = (20 - 8)(15 - 8) = 12 \times 7 = 84 \text{ m}^{2} \]
\[ A_{\text{path}} = 300 - 84 = 216 \text{ m}^{2} \]
\[ \text{cost} = 216 \times 6 = \text{Rs. } 1296 \]
Subtracting only 4 m from each dimension rather than 8 is the standard error - the path runs along both opposite sides.
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