A train travels at a certain average speed for a distance of 63 km and then travels a distance of 72 km at an average speed of 6 km/h more than its original speed. If it takes 3 hours to complete the total journey, what is the original speed of the train in km/h ?
- A.24
- B.33
- C.42
- D.66
▶ Answer & Explanation
Correct answer: C. 42
Let the original speed be 's' km/h. The time taken for the first 63 km is 63/s. The time taken for the next 72 km at a speed of (s+6) km/h is 72/(s+6). The total time is given as 3 hours. Thus, the equation is 63/s + 72/(s+6) = 3. Solving this equation leads to a quadratic equation, and the positive integer solution for 's' is 42 km/h. This speed satisfies the conditions of the problem, with the times for each segment adding up to 3 hours.
Source: UPSC csat 2013