A person goes to college at a speed of 4 km/hr and gets late by 15 minutes. If he had travelled at 5 km/hr, he would have got late by 9 minutes. What should be his speed such that he reaches his college 10 minutes early?
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45 km/hr
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24 km/hr
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52 km/ hr
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18 km/hr
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None of these
B
Correct answer
Explanation
Let distance be d. Time taken at 4 km/hr = d/4. Time taken at 5 km/hr = d/5. Difference = (d/4 - d/5) = 15 - 9 = 6 mins = 0.1 hr. d/20 = 0.1, d = 2 km. Time to reach on time = d/4 - 15/60 = 0.5 - 0.25 = 0.25 hr. To reach 10 mins early, time = 0.25 - 10/60 = 0.25 - 0.166 = 0.0833 hr. Speed = 2 / 0.0833 = 24 km/hr.