Question

A bus driver completes a trip of \[180{\text{ }}km\] in \[4{\text{ }}hrs.\] If he averages \[50{\text{ }}km/hr\]during the first \[3{\text{ }}hrs\] of trip, then his speed in the final hour is
A) \[45{\text{ }}km/hr\]
B) \[35{\text{ }}km/hr\]
C) \[50{\text{ }}km/hr\]
D) \[30{\text{ }}km/hr\]

Answer 1

Hint: To solve this question, we will need to get the distance left for final hour. And then using that distance and time we will get the required speed.

Complete step-by-step answer:
We have been given that a bus driver took \[4{\text{ }}hrs\]for a trip of \[180{\text{ }}km.\]
So, total distance covered by driver \[ = {\text{ }}180{\text{ }}km\]
And the time taken by him to cover \[180{\text{ }}km{\text{ }} = {\text{ }}4{\text{ }}hrs\]
We are also been given that the average speed during \[3{\text{ }}hrs\] of trip \[ = {\text{ }}50{\text{ }}km/hr\]
We know that, \[Distance{\text{ = speed}} \times time\] $ $
So, distance covered by him in \[3{\text{ }}hrs\]\[ = {\text{ }}3 \times 50{\text{ }} = {\text{ }}150{\text{ }}km\]
Now, distance left for final hour \[ = {\text{ }}180{\text{ }}-{\text{ }}150{\text{ }} = {\text{ }}30{\text{ }}km\]
And the time taken to cover that \[30{\text{ }}km\]\[ = {\text{ }}4 - 3{\text{ }} = {\text{ }}1{\text{ }}hr\]
We know that, $ Speed = \dfrac{{Distance}}{{Time}} $
Now, the driver’s speed in the final hour $ = \dfrac{{30}}{1} $ $ = 30km/hr $
Thus, option (D) \[30{\text{ }}km/hr,\] is the correct answer.
So, the correct answer is “Option D”.

Note: Students should take care that we need to get the speed for the final hour only, so only distance left for that final hour is required. Students should not get confused about using the whole distance for it.