Question
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A road 3.5 m wide surrounds a circular plot whose circumference is 44 m . Find the cost of paving the road at \( ₹ 20 \) per \( \mathrm{m}^{2} \). (Take \( \pi=\frac{22}{7} \) )

Ask by Gough Huff. in India
Jan 27,2025

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Answer

The cost of paving the road is ₹3,850.

Solution

To determine the cost of paving the road surrounding the circular plot, follow these steps: 1. **Find the Radius of the Inner Circle (Plot):** Given the circumference of the inner circle: \[ \text{Circumference} = 44 \, \text{m} = 2\pi r_{\text{inner}} \] Solving for \( r_{\text{inner}} \): \[ r_{\text{inner}} = \frac{44}{2\pi} = \frac{44}{2 \times \frac{22}{7}} = 7 \, \text{m} \] 2. **Determine the Outer Radius:** The road is 3.5 m wide, so: \[ r_{\text{outer}} = r_{\text{inner}} + 3.5 = 7 + 3.5 = 10.5 \, \text{m} \] 3. **Calculate the Area of the Road:** The area of the road is the area of the outer circle minus the area of the inner circle: \[ \text{Area} = \pi \left( r_{\text{outer}}^2 - r_{\text{inner}}^2 \right) \] Substituting the values: \[ \text{Area} = \frac{22}{7} \left( 10.5^2 - 7^2 \right) = \frac{22}{7} \left( 110.25 - 49 \right) = \frac{22}{7} \times 61.25 = 192.5 \, \text{m}^2 \] 4. **Compute the Cost of Paving:** Given the cost is ₹20 per m²: \[ \text{Total Cost} = 192.5 \times 20 = ₹3,850 \] **Final Answer:** ₹ 3,850

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To find the cost of paving the road, let's first calculate the radius of the circular plot. Using the formula for circumference \( C = 2\pi r \), we can rearrange it to find the radius. Given \( C = 44 \) m and \( \pi = \frac{22}{7} \): \[ 44 = 2 \times \frac{22}{7} \times r \implies r = \frac{44 \times 7}{2 \times 22} = 7 \, \text{m} \] The width of the road is 3.5 m, so the radius of the outer edge of the road is \( 7 + 3.5 = 10.5 \, \text{m} \). Next, we find the area of the road: 1. Area of the larger circle (including the road): \[ A_1 = \pi (10.5)^2 = \frac{22}{7} \times 110.25 = 346.5 \, \text{m}^{2} \] 2. Area of the smaller circle (the plot): \[ A_2 = \pi (7)^2 = \frac{22}{7} \times 49 = 154 \, \text{m}^{2} \] 3. Area of the road: \[ A_{road} = A_1 - A_2 = 346.5 - 154 = 192.5 \, \text{m}^{2} \] Now, to find the cost of paving the road: \[ \text{Cost} = 192.5 \, \text{m}^{2} \times ₹ 20 = ₹ 3850 \] Thus, the cost of paving the road is **₹ 3850**.

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