Time and Distance – Opposite-walking problem (meeting time): Two persons A and B are 20 km apart. A walks at 4 km/h and B at 6 km/h. Starting at 7:00 a.m., they walk towards each other. At what time will they meet?

Introduction / Context:
In opposite-direction motion, relative speed is the sum of the individual speeds. Divide the initial separation by the relative speed to obtain the meeting time interval, then add it to the start time.

Given Data / Assumptions:

• Distance between A and B = 20 km.
• Speeds: 4 km/h (A) and 6 km/h (B).
• Start time = 7:00 a.m.

Concept / Approach:
Relative speed = 4 + 6 = 10 km/h. Time to meet = distance / relative speed.

Step-by-Step Solution:
Time = 20 / 10 = 2 hours.Meeting time = 7:00 a.m. + 2 hours = 9:00 a.m.

Verification / Alternative check:
In 2 hours, A covers 8 km and B covers 12 km; 8 + 12 = 20 km, matching the initial separation.

Why Other Options Are Wrong:
8:00 a.m. and 8:30 a.m. are too early; 10:00 a.m. is too late; 7:48 a.m. is unrealistic given the low speeds.

Common Pitfalls:
Confusing relative speed (sum here) with difference (used for same-direction problems).

Final Answer:
9:00 am