Question

By walking at \(\dfrac{4}{5}\) of his usual speed, a man reaches office 10 minutes later than usual. What is his usual time?

• A. 20 min
• B. 40 min
• C. 30 min
• D. 50 min

Hint:

If speed drops to 4/5, time rises to 5/4 of usual; the 1/4 extra equals the given 10-minute delay.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept.
Speed and time are inversely proportional when distance is fixed, so if speed becomes \(\dfrac{4}{5}\) of usual, time becomes \(\dfrac{5}{4}\) of usual.

Step 2: Set up the equation.
Let the usual time be \(T\) minutes. New time \(=\dfrac{5}{4}T\).

Step 3: Use the given delay.
The extra time taken is 10 minutes: \(\dfrac{5}{4}T - T = 10 \Rightarrow \dfrac{1}{4}T = 10 \Rightarrow T = 40\).

Step 4: Final Answer.
The usual time is 40 minutes, so option B is correct.