Correct Answer - Option 1 : 89 km / h (approx.)
Given∶
Average speed while going from X to Y = 80 km / h
Average speed while coming back = 100 km / h
Formula Used∶
Average = Sum of observations / Number of observations
Time = Distance / speed
Calculation∶
Let the distance XY = a km
Average speed while going from X to Y = 80 km / h
Time taken to cover a km from X to Y = (a / 80) hours
Average speed while coming back from Y to X = 100 km / h
Time taken to cover a km from Y to X = (a / 100) km / h
Total time taken to cover 2a km = (a / 80) + (a / 100) = (9a / 400) hours
Average speed = Total Distance / Total Speed = 2a / (9a / 400) = 88.88 km / h = 89 km / h(approx.)
∴ The speed of the bike during the whole journey is 88.88 km / h or 89 km / h (approx.).