A man rides at the speed of 15 km/hr, but stops for 5 min to change horse at the end of every 8 km. Find the time taken by him to cover the distance of 90 km.

 6 hours 55 minutes

Speed = 15km/hr

Distance = 90km

Minimum time without stoppage = \(\frac{90}{15}\) = 6hrs.

If he stops for 5 mins. after every 8 km , then to cover 90km , he will stop for at least 11 times.

So, total stoppage time = 11 × 5 = 55 min 

Total time taken to cover 90 km = 6 hours + 55 minutes = 6 hours 55 minutes