A’s speed is 1 3/8 times B’s speed (that is, 11/8 of B). In a race, A gives B a start of 300 m and they finish together. What should be the total race length (distance A runs) so both reach the winning post simultaneously?

Difficulty: Easy

Correct Answer: 1,100 m

Explanation:


Introduction / Context:
When a faster runner gives a head-start but still aims to finish together, the time equality relates the full distance for the faster to the reduced distance for the slower via their speed ratio.



Given Data / Assumptions:

  • vA = (11/8) vB.
  • B’s head-start = 300 m.
  • Let race length (A’s distance) be L; B runs L − 300.


Concept / Approach:
Equal finish times: L / vA = (L − 300) / vB. Substitute vA and solve for L.



Step-by-Step Solution:

L / ((11/8) vB) = (L − 300)/vB ⇒ (8L/11) = L − 300.Multiply by 11: 8L = 11L − 3,300 ⇒ 3L = 3,300 ⇒ L = 1,100 m.


Verification / Alternative check:
Times become equal: A’s time = 1,100 / (11/8 vB) = 800 / vB; B’s time = 800 / vB.



Why Other Options Are Wrong:
Other lengths do not satisfy the derived equality.



Common Pitfalls:
Subtracting 300 from the faster runner’s distance, or inverting the 11/8 ratio.



Final Answer:
1,100 m

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