Two runners start from the same point on a 4,200 m circular stadium and run in opposite directions at 500 m/min and 700 m/min. After how many minutes will they meet each other?

Introduction / Context:
When two runners move towards each other on a circular track from the same point in opposite directions, they meet when their combined distance equals one full circumference. Use relative speed (sum) to find the meeting time.

Given Data / Assumptions:

• Circumference = 4,200 m.
• Speeds: 500 m/min and 700 m/min.

Concept / Approach:
Relative speed (opposite directions) = 500 + 700 = 1,200 m/min. Meeting time = distance / relative speed = 4,200 / 1,200.

Step-by-Step Solution:

Verification / Alternative check:
Positions after 3.5 min: 500×3.5 = 1,750 m; 700×3.5 = 2,450 m; total = 4,200 m ⇒ meet.

Why Other Options Are Wrong:
Other times misapply relative speed or circumference.

Common Pitfalls:
Using difference of speeds (appropriate for same direction), not the sum.

Final Answer:
3.5 minutes