A car goes from a town A to another town B with a speed of 40km/hr and returns back to town A with a speed of 60 km/hr the average speed of the car during the complete journey is
Answers
Answer:-
Let the distance between town A & B be "d".
Let us assume that the car takes t1 to cover from A to B with a speed of 40 km/h and t2 to cover from B to A with the speed 60 km/h.
We know that,
Time = Distance/speed
Hence,
→ t1 = (d/40) hrs.
and,
→ t2 = (d/60) hrs.
We know that,
Average speed = (Total distance travelled) / total Time taken
- Total Distance = d + d
- Total time taken = t1 + t2
→ Average speed of the car = (d + d) / [ (d/40) + (d/60) ]
→ Average speed of the car = 2d / [ (3d + 2d) / 120 ]
→ Average speed of the car = 2d / [(5d) / 120]
→ Average speed of the car = 2d * (120/ 5d)
→ Average speed of the car = 48 km/h
Hence, the Average speed of the car is 48 km/hr.
Explanation:
Assume that the distance covered by the car is x km.
Time = Distance/Speed
t1 = x/40 hr and t2 = x/60 hr
Total distance covered = x + x = 2x km
Total time taken = t1 + t2 = x/40 + x/60 = (3x + 2x)/120 = x/24 hr
Average speed = (Total distance covered)/(Total time taken)
= 2x/(x/24)
= 48 km/hr
Hence, the average speed of the car is 48 km/hr.
Shortcut Method
Average speed = (2 × s1 × s2)/(s1 + s2)
= (2 × 40 × 60)/(40 + 60)
= 4800/100
= 48 km/hr