Multiple choice

A train travels a distance of 300 km. at a constant speed. If the speed of the train is increased by 5 km. an hour, the journey would have taken 2 hours less. Find the original speed of the train. एक रेलगाड़ी 300 किमी. की दूरी एक नियत चाल से तय करती है । यदि रेलगाड़ी की चाल 5 किमी. प्रति घंटा बढ़ा दी जाये तो यात्रा में दो घण्टे कम समय लगता है, तो रेलगाड़ी की प्रारम्भिक चाल ज्ञात कीजिए।

  1. 30 km./hr. / किमी./घं.

  2. 25 km./hr. / किमी./घं.

  3. 24 km./hr. / किमी./घं.

  4. 20 km./hr. / किमी./घं.
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B Correct answer
Explanation

Let original speed be v kmph. Time at original speed = 300/v hours. Time at increased speed = 300/(v+5) hours. Difference: 300/v - 300/(v+5) = 2. Solving: 300(v+5-v)/v(v+5) = 2, giving v²+5v-750=0, so (v+30)(v-25)=0, hence v=25 kmph. Verification: 300/25=12 hours, 300/30=10 hours, difference=2 hours.

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