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.).**