In a journey of 240 km, a bus covers a distance of 150 km at the speed of 75 km/h, the next 60 km distance at the speed of 100 km/h and the remaining distance at the speed of 75 km/h. The average speed (in km/h) of the bus for the whole journey is:

Given:

Total distance = 240 km

Distance₁ = 150 km, Speed₁ = 75 km/h

Distance₂ = 60 km, Speed₂ = 100 km/h

Remaining distance = 240 - 150 - 60 = 30 km, Speed₃ = 75 km/h

Formula Used:

Time = Distance / Speed

Average Speed = Total Distance / Total Time

Calculation:

Time taken for the first part (T₁) = Distance₁ / Speed₁ = 150 / 75 = 2 hours

Time taken for the second part (T₂) = Distance₂ / Speed₂ = 60 / 100 = 0.6 hours

Time taken for the third part (T₃) = Remaining distance / Speed₃ = 30 / 75 = 0.4 hours

Total time taken (T) = T₁ + T₂ + T₃ = 2 + 0.6 + 0.4 = 3 hours

Average Speed = Total Distance / Total Time = 240 / 3 = 80 km/h

The average speed of the bus for the whole journey is 80 km/h.