A man started 15 minutes late and by travelling at a speed which is 5/...
Explanation:
Let's assume that the usual time of the journey is 't' hours and the distance to the office is 'd' km.
Given:
The man started 15 minutes late = 1/4 hour
He reached 20 minutes early = 1/3 hour
His speed was 5/4th of his usual speed
Formula:
Speed = Distance/Time
Calculation:
Let's first calculate the time taken by the man to reach the office if he started on time and travelled at his usual speed.
Usual time = t hours
Usual speed = Distance/Time = d/t
Time taken = t + 1/3 (as he reached 20 minutes early)
Distance = Speed * Time = (d/t) * (t + 1/3) = (3d + t)/3
Now, let's calculate the time taken by the man if he started 15 minutes late and travelled at 5/4th of his usual speed.
New speed = (5/4) * (d/t) = (5d/4t)
New time = (d/(5d/4t)) = (4t/5) hours
Time taken = t - 1/4 + 4/15 (as he reached 20 minutes early)
Distance = Speed * Time = ((5d/4t) * (4t/5)) = d
Since the distance travelled in both cases is the same, we can equate the two distances.
(3d + t)/3 = d
3d + t = 3d
t = 100
Therefore, the usual time of the journey is 100 hours.