Driving at \(\frac{4}{5}\) of his usual speed, a man reaches his destination 15 minutes later than usual. What is his usual time (in minutes) for the journey?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 60
For a fixed distance, time is inversely proportional to speed. At \(\frac{4}{5}\) of the speed, the time becomes \(\frac{5}{4}\) of the usual time.
Let the usual time be \(T\) minutes; the new time is \(\frac{5}{4}T\)
Extra time \(\displaystyle =\frac{5}{4}T-T=\frac{T}{4}=15\)
\(T=60\) minutes