A bus during its journey travels 60 minutes at a speed of 80 km/h, another 90 minutes at a speed of 100 km/h, and 4 hours at a certain speed. If the average speed of the bus during its whole journey is 70 km/h, what is the speed of the bus during the 4 hours?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 56.25 km/h.
60 minutes = 1 hour and 90 minutes = 1.5 hours
First distance = 80 × 1 = 80 km
Second distance = 100 × 1.5 = 150 km
Let speed for the last segment = x km/h
(80 + 150 + 4x)/(1 + 1.5 + 4) = 70
⇒ (230 + 4x)/6.5 = 70
⇒ 230 + 4x = 455
⇒ 4x = 225
⇒ x = 225/4 = 56.25 km/h