Question

Lee and Sheby race clockwise around a 400 meter oval

Track. They start from the same place at the same time. Lee
runs at a speed of 72 kiometers per hour and Shelby runs at
a speed of 9 kilometers per hour. How many meters must
Shelby run to cover exactly 3 more laps than Lee in the same
time?

Answer 1

6,000 meters

Explanation:

Length of one lap d = 400 m

Lee's speed = u = 7.2 km/h. Shelby's speed v = 9 km/h

After time t, Shelby will run x meters to cover exactly 3 more laps than Lee.

So x = vt

and

x - 3d = ut

Note t = x/v, then

x - 3d = x*u/v

x (1 - u/v) = 3d

x = 3d/(1 - u/v) = 3*400/(1 - 7.2/9) = 6,000 meters