Sum
The radii of the inner and outer circumferences of a circular running track are 63 m and 70 m respectively. Find :
(i) the area of the track ;
(ii) the difference between the lengths of the two circumferences of the track.
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Solution
Outer radius, r1 = 70 m
Inner radius, r2 = 63 m
∴ Area of track = `pir_1^2 - pir_2^2`
= `22/7[(70)^2 - (63)^2]`
= `22/7(70 + 63)(70 - 63)`
= `22/7 xx 133 xx 7`
= 2926 m2
Length of outer edge i.e. circumference
= `2pir_1`
= `2 xx 22/7 xx 70 = 440`m
Length of inner edge = `2pir_2`
= `2 xx 22/7 xx 63 = 396` m
Difference between lengths of two circumferences = 440 – 396 = 44 m
Hence (i) 2926 m2 (ii) 44 m
Concept: Area of Circle
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