alleryA train covers 360 km at uniform speed. If the speed were 5 km/h more, it would take 1 hour less. The actual speed is
A40 km/h
B30 km/h
C45 km/h
D60 km/h
Answer & Solution
Correct answer: A. 40 km/h
1. Let speed be v km/h; time = 360/v hours.
2. New time equation: 360/v - 360/(v + 5) = 1.
3. Multiply through: v^2 + 5v - 1800 = 0.
4. Factor (v - 40)(v + 45) = 0, take v = 40 km/h.
_Source: Selina Concise Mathematics Class 10, Ch 5 Quadratic Equations (Mistral OCR'd PDF), section on speed-time problems_
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