A square track has each side of length 1 km. A man travels the first two sides…

Average speed over a multi-segment trip is total distance divided by total time -- it is NOT the average of the individual segment speeds. When a speed is given in mph alongside others in kmph, convert using the standard approximation 1 mph = 1.6 kmph.

1. Total distance for the square track = 4 sides x 1 km = 4 km.

2. Total time allowed for an average speed of 60 kmph over 4 km = 4 / 60 hour = 4 minutes.

3. Speed for the first two sides = 30 mph = 30 x 1.6 = 48 kmph. Time for these 2 km = 2 / 48 hour = 2.5 minutes.

4. Time for the third side (1 km) at 60 kmph = 1 / 60 hour = 1 minute.

5. Time used for the first three sides = 2.5 + 1 = 3.5 minutes.

6. Time left for the fourth side = 4 - 3.5 = 0.5 minutes = 1/120 hour.

7. Speed needed for the fourth side (1 km) = 1 / (1/120) = 120 kmph.

Check: total time = 2.5 + 1 + 0.5 = 4 minutes for 4 km, which gives an average speed of 4 km / (4/60 hour) = 60 kmph, confirming the answer.