Difficulty: Medium
Correct Answer: 60 km/h
Explanation:
Introduction / Context:
This problem tests weighted time calculations with different speeds on two legs of a round trip and a fixed halt. Translating words into equations and keeping careful units is the key.
Given Data / Assumptions:
Concept / Approach:
If return speed is v, onward speed is 1.25v. Travel time = 800/(1.25v) + 800/v. Add the 2 h halt and set equal to 32 h.
Step-by-Step Solution:
Verification / Alternative check:
At v = 48, times are 640/48 = 13.333… h and 800/48 = 16.666… h. Sum = 30 h; plus 2 h halt = 32 h as required.
Why Other Options Are Wrong:
Values like 56.25, 66.50, or 67 km/h violate the time equation after including the halt; they do not total 32 h.
Common Pitfalls:
Forgetting the halt, or assuming 1600 km is one-way. Also mixing up “25% more speed” with “25% less time” can lead to algebra errors.
Final Answer:
60 km/h
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