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There is a road of equal width all around a circular garden. The outer and inner circumferences of the road are 328 m and 200 m respectively. The area of the road will be :

  1. 5376 m2

  2. 5375 m2

  3. 5374 m2

  4. 5373 m2

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Answer

There is a road of equal width all around a circular garden. The outer and inner circumferences of the road are 328 m and 200 m respectively. The area of the road will be. Circumference & Area of a Circle, R.S. Aggarwal Mathematics Solutions ICSE Class 9.

Outer circumference (C1) = 328 m

Inner circumference (C2) = 200 m

Circumference = 2π.radius

Let outre radius be R meters and inner radius be r meters.

Calculating outer circumference,

Outer circumference=2×227×R328=2×227×RR=328×744=57411 m\Rightarrow \text{Outer circumference} = 2 \times \dfrac{22}{7} \times R \\[1em] \Rightarrow 328 = 2 \times \dfrac{22}{7} \times R \\[1em] \Rightarrow R = \dfrac{328 \times 7}{44} = \dfrac{574}{11} \text{ m}

Calculating inner circumference,

Inner circumference=2×227×r200=2×227×rr=200×744r=35011 m.\Rightarrow \text{Inner circumference} = 2 \times \dfrac{22}{7} \times r \\[1em] \Rightarrow 200 = 2 \times \dfrac{22}{7} \times r \\[1em] \Rightarrow r = \dfrac{200 \times 7}{44} \\[1em] \Rightarrow r = \dfrac{350}{11} \text{ m}.

Area = π(R2 - r2)

= π(R + r)(R - r)

=227×(57411+35011)×(5741135011)=227×92411×22411=2×84×32=5376 m2.= \dfrac{22}{7} \times \Big(\dfrac{574}{11} + \dfrac{350}{11}\Big) \times \Big(\dfrac{574}{11} - \dfrac{350}{11}\Big) \\[1em] = \dfrac{22}{7} \times \dfrac{924}{11} \times \dfrac{224}{11} \\[1em] = 2 \times 84 \times 32 \\[1em] = 5376 \text{ m}^2.

Hence, option 1 is the correct option.

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