Question

find the area of a circular running made by two concentric circle of radii 7cm and 10.5 cm​

Answer 1

Answer:

The area enclosed by two concentric of radii r

1

and r

2

(r

1

>r

2

)=π(r

1

2

−r

2

2

)

⇒ Thus, the area enclosed by two inner concentric circles =π[(7)

2

−(3.5)

2

]

⇒ The area enclosed by two inner concentric circles =

7

22

×(49−12.25)

⇒ The area enclosed by two inner concentric circles =

7

22

×36.75=115.5cm

2

According to the given information,

⇒ π[(r

2

−(7)

2

]=π[(7)

2

−(3.5)

2

]

⇒ r

2

=[7

2

+7

2

−(3.5)

2

]

⇒ r

2

=(3.5)

2

×(4+4−1)

⇒ r

2

=7×(3.5)

2

⇒ r

2

=85.75

∴ r=9.26cm