There are two concentric circular track of radii 100m and 102m, respectively . A runs on the inner track and goes once round in 1 min 30 sec, while B runs on the outer track in 1 min 32 sec. Who runs faster?

First let us take out the circumferences of both circles.

Radius of inner circle = 100 m

∴Circumference of the inner track= 2πr

                                                    = 2×3.14×100

                                                    = 628 m 

Radius of outer track= 102 m

So, Circumference of outer track=2πr = 2×3.14×102 = 753.6 m

Time taken by A = 1 min 30 sec = 90 sec

Time taken by B = 1 min 32 sec = 92 sec

Speed of A = Distance covered by A/ Time taken 

                    = 628/90

                    = 6.98 m/s

Speed of B = Distance covered by B /time taken 

                   =753.6/92

                   =8.19 m/s

  Speed of A is smaller than the speed of B.

  So, B runs faster.