Question

a well of diameter 150 cm has a 30 cm wide parapet running around it find the area of parapet
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Answer 1

Answer:

Didn't understood your question correctly.

Answer 2

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Diameter of well = 150 cm

Radius of well = 150/2 =75cm

Width of parapet = 30 cm

Now, parapet of the well forms two circles.

One is inner circle and second is outer circle.

Radius of inner circle r = 75 cm

Radius of outer circle R = inner radius + width of parapet = 75 + 30 = 105 cm

Area of parapet = Area of outer circle - Area of inner circle

$= πR {}^{2} −πr {}^{2} \\ =π(R {}^{2} −r {}^{2} ) \\ =  \frac{22}{7} [(105) {}^{2} −(75) {}^{2} ] \\ =  \frac{22}{7} ×5400 \\ =  \frac{118800}{7} cm {}^{2} \\ =16971.428cm {}^{2}$

Hence,the area of Parapet is 16971.428cm^2