RRB JE practice question
A train covers 80 km at a certain speed and then covers the next 120 km at a speed 20 km/h more than the first. If the total time taken is 4 hours, find the original speed.
From a RRB JE Quantitative Aptitude practice set · Quantitative Aptitude
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Correct answer: (A) 40 km/h
Let the original speed = u km/h.
80/u + 120/(u+20) = 4
80(u+20) + 120u = 4u(u+20)
80u + 1600 + 120u = 4u² + 80u
200u + 1600 = 4u² + 80u
4u² − 120u − 1600 = 0
u² − 30u − 400 = 0
u = [30 + √(900+1600)]/2 = [30 + 50]/2 = 40.
Original speed = 40 km/h.
हिंदी में प्रश्न
एक ट्रेन 80 किमी की दूरी एक निश्चित गति से तय करती है और फिर अगले 120 किमी की दूरी पहली गति से 20 किमी/घंटा अधिक गति से तय करती है। यदि कुल समय 4 घंटे लगता है, तो मूल गति ज्ञात कीजिए।
उत्तर जाँचने के लिए किसी विकल्प पर टैप करें।
उत्तर और व्याख्या देखें
सही उत्तर: (A) 40 किमी/घंटा
मान लीजिए मूल गति u किमी/घंटा है।
80/u + 120/(u+20) = 4
80(u+20) + 120u = 4u(u+20)
80u + 1600 + 120u = 4u² + 80u
200u + 1600 = 4u² + 80u
4u² − 120u − 1600 = 0
u² − 30u − 400 = 0
u = [30 + √2500]/2 = [30 + 50]/2 = 40।
मूल गति = 40 किमी/घंटा।
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