A girl while walking diametrically across a semicircular playground, takes 3 minutes less than if she had kept walking round the circular path from A to B. If she walks 60 metres a minute, what is diameter of the play ground?

Explanation:-

Let the radius be r, then difference in the distance,
∏r - 2r = r (∏ - 2)
= r [(3.14) -2] = 60 *3
2r = 315 m. [∏r = semi perimeter, 2r = diameter]