Amit walks at 4 km/h. Four hours later, Brijesh starts from the same point on a bicycle at 20 km/h. At what distance from the start will Brijesh catch Amit?

Introduction / Context:
This is a pursuit (catch-up) problem on a straight path. The early head start distance equals the product of Amit’s speed and the lead time. The catch-up time then depends on relative speed.

Given Data / Assumptions:

• Amit speed = 4 km/h; Brijesh speed = 20 km/h.
• Lead start = 4 hours for Amit.

Concept / Approach:
Head start distance = 4 km/h × 4 h = 16 km. Relative speed = 20 − 4 = 16 km/h. Time to catch after Brijesh starts = head start / relative speed = 1 hour. Position from start = Amit’s total time × 4 km/h (or Brijesh’s 1 hour × 20 km/h).

Step-by-Step Solution:

Verification / Alternative check:
Both computations give 20 km, confirming the meeting point.

Why Other Options Are Wrong:
15, 18, 24, 13 km do not satisfy head-start and relative-speed logic.

Common Pitfalls:
Forgetting to use relative speed; miscalculating the 4-hour head start distance.

Final Answer:
20 km