Question

The area of a circular ring enclosed between two concentric circles is 286 cm . Find the

2

radius of the inner circle if the radius of the outer circle is given to be 10cm.​

Answer 1

Answer:

The distance around the circular region is called its circumference. The ratio of circumference of any circle to its diameter is constant. This constant is denoted by π and is read as pie.

Circumference/Diameter = Pie

i.e., c/d = π   or   c = πd

We know that diameter is twice the radius, i.e., d = 2r

    C = π × 2r

⇒ C = 2πr

Therefore approximate value of π = 22/7 or 3.14.

Answer 2

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Area of outer circle - area of inner circle = 286 sqcm

Pi(r1² - r2²) = 286 sqcm

Pi(r1 - r2) (r1 + r2) = 286

Pi × 7 × (r1 + r2) = 286

r1 + r2 = 286/22= 13

Now by solving 2 equations simultaneously

r1 + r2 = 13

r1 - r2 = 7

You get r1 = 10cm, r2=7cm