Multiple choice

A bike travels a distance of 200 km. at a constant speed. If the speed of bike is increased by 5 km. an hour, the journey would have taken 2 hours less. What is the speed of bike? एक बाइक 200 किमी. की दूरी पर नियत चाल से चलती है। यदि बाइक की चाल में 5 किमी. प्रति घंटा की वृद्धि कर दी जाए तो यात्रा में 2 घंटे समय कम लगता है। बाइक की चाल क्या है?

  1. 30 km./hr./किमी./ घंटा

  2. 25 km./hr./किमी./ घंटा

  3. 20 km./hr./किमी./ घंटा

  4. 15 km./hr./किमी./ घंटा
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C Correct answer
Explanation

Let original speed be x km/hr. Original time = 200/x hours. New speed = x + 5 km/hr. New time = 200/(x+5) hours. Difference is 2 hours: 200/x - 200/(x+5) = 2. Solving: 200(x+5) - 200x = 2x(x+5). 1000 = 2x² + 10x. x² + 5x - 500 = 0. (x + 25)(x - 20) = 0. x = 20 (positive root). Original speed is 20 km/hr.

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