Moving at of its usual speed, a bus is 20 minutes late. What is its usual time to cover the journey?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 2 hours.
Let the usual time to cover the journey be t minutes
The speed of the bus is reduced to 6/7 of its usual speed.
Since time and speed are inversely proportional, the time taken when the bus moves at 6/7 of its usual speed is 7/6 of the usual time.
Therefore,
The time taken at the reduced speed = 7/6 × t
Now,
The bus is 20 minutes late, so the difference between the time taken at the reduced speed and the usual time is 20 minutes
7t/6 - t = 20
⇒ (7t - 6t)/6 = 20
⇒ t/6 = 20
⇒ t = 120
Thus, the usual time to cover the journey is 120 minutes or 2 hours.