Question

a man cycles from A to B a distance of 21 km in 1 hour 40 minutes the road from A is level for  13 km and then it  is uphill to B. the man's average speed on level is 15k'/hr find his average uphill speed?

Answer 1

Man takes (13/15)*60=52 minutes to cover distance of 13 km. Then in the remaining 48 minutes he has to cover 8 km i.e. (8/48)=1/6 km/min i.e 10 km/hr.

Answer 2

Given:

(i) The man cycles from A to B.

(ii) The total distance is 21 km and time taken is 1 hour 40 minutes

(iii) The road from A is level for 13km and then uphill to B

(iv) His average speed on level is 15 km/hr.

To find:

(i) Average uphill speed

Solution:

Total distance is 21 km.

Total time taken = 1 hour 40 mins

= 5/3 hours                           [Representing 40 mins in hours as 40/60 = 2/3]

= 100 minutes

Distance travelled on level road = 13km

Speed = 15km/hr.

So, time taken = Distance/Speed

= (13/15) hours

= 0.867 hours

= 52 minutes

So, distance of the uphill road = Total distance - Level road distance

= (21 - 13)km

= 8 km

Total time taken on uphill road  =  Total time - Time on level road

= (100 - 52)mins

= 48 mins

= 0.8 hours

So, average speed = Distance/Time

= (8/0.8) km/hr

= 10 km/hr

His average uphill speed is 10 km/hr.