Two trains start at the same time from Kolkata and Patna towards each other. After they pass, the Kolkata train needs 6 h 15 min and the Patna train 4 h to finish. The Patna train runs at 75 km/h. What is the Kolkata train's speed?

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Accepted Answer

60 km/h. Speeds are in the ratio of the square roots of the opposite times: Kolkata : Patna =√4:√6.25=2:2.5. Kolkata train =75×2/2.5=60 km/h. (48 km/h uses the plain time ratio.)

Two trains start at the same time from Kolkata and Patna towards each other. After they pass, the Kolkata train needs 6 h 15 min and the Patna train 4 h to finish. The Patna train runs at 75 km/h. What is the Kolkata train's speed?

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