Question

The radii of two circles are 25 cm and 18 cm. Find the radius of the circle which has a circumference equal to the sum of circumferences of these two circles. 

Answer 1

Circumference of the first circle

S₁ = 2π x 25
     = 50π cm

Circumference of the second circle

S₂ = 2π x 18
     = 36π cm

Let r be the radius of the resulting circle.
2πr = 50π + 36π
2πr = 86π

r = `(86π)/(2π)`
  = 43 cm