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Find the area and the perimeter of the shaded region in figure (i) given below. The dimensions are in centimeters.

Find the area and the perimeter of the shaded region in figure. Mensuration, ML Aggarwal Understanding Mathematics Solutions ICSE Class 9.

Mensuration

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Answer

From figure,

Radius of larger semi-circle (R) = 14 cm.

Area of larger semi-circle = πR22=227×(14)2×12\dfrac{πR^2}{2} = \dfrac{22}{7} \times (14)^2 \times \dfrac{1}{2}

=227×196×12= \dfrac{22}{7} \times 196 \times \dfrac{1}{2}

= 22 × 14

= 308 cm2.

Diameter of smaller semi-circle = 14 cm; radius (r) = 142\dfrac{14}{2} = 7 cm.

Area of smaller semi-circle = πr22=227×(7)2×12\dfrac{πr^2}{2} = \dfrac{22}{7} \times (7)^2 \times \dfrac{1}{2}

=227×49×12= \dfrac{22}{7} \times 49 \times \dfrac{1}{2}

= 11 × 7

= 77 cm2.

From figure,

Area of shaded region = Area of larger semi-circle - Area of smaller semi-circle

= 308 - 77

= 231 cm2.

From figure,

Perimeter of shaded region = Circumference of larger semi-circle + Circumference of smaller circle + 14

= πR + πr + 14

= 227×14+227×7+14\dfrac{22}{7} \times 14 + \dfrac{22}{7} \times 7 + 14

= 44 + 22 + 14

= 80 cm.

Hence, area of shaded region = 231 cm2 and perimeter = 80 cm.

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