Question

A car travels 100 km at a speed of 60 kmh and returns with a speed of 40kmh calculate the average speed for the whole journey

Answer 1

Answer:

Step-by-step explanation:

=> Here, Distance covered by car while going and returning is equal.

∴ D_1 = D_2 = 100 km

=> Time for first leg T_1 : 60 km/ hr for 100 km is 100/60 = 1.67 hr

=> Time for second leg T_2 : 40 km/hr for 100 km is 100/40= 2.5 hr

=> Total time T = T_1 + T_2 = 1.67 + 2.5 hrs = 4.17

=> Total Distance D =  D_1 + D_2 = 100 + 100 = 200 km  

=> Average speed = D/T = 200/4.17= 47.96 km/hr ≃ 48 km/hr

Therefore,  the average speed for the whole journey is approx 48 km / hr.  

Answer 2

Answer:

48 km/hr

Step-by-step explanation:

Distance one side = 100 km

Speed one side = 60 km/h

time taken one side = Distance/speed = 100/60 hr

= (100/60)*60 = 100 mins

Speed return = 40 km/h

time taken one side = Distance/speed = 100/40 hr

= (100/40)*60 = 150 mins

Total time take = 100 + 150 = 250 min

= 250/60 hr

= 25/6 hr

Total distance = 100 + 100 = 200 km

Average speed = 200/(25/6) = 48 km/hr