CA Foundation · Quantitative Aptitude · Equations
A train travels 240 km at a uniform speed. If its speed had been 20 km/h more, the journey would have taken 1 hour less. What is the original speed of the train?
The original speed is 60 km/h. Setting 240/x − 240/(x+20) = 1 gives x²+20x−4800=0, whose positive root is 60. Check: the journey takes 4 hours at 60 km/h and 3 hours at 80 km/h, which differ by exactly 1 hour.
- A50 km/h
- B60 km/h
- C40 km/hCorrect
- D80 km/h
Explanation
Let speed be x. Then 240/x − 240/(x+20) = 1, so 240×20 = x(x+20), giving x²+20x−4800=0. Factorising: (x+80)(x−60)=0, so x=60 (negative rejected). Check: 240/60=4 h and 240/80=3 h, a difference of 1 hour. The value 80 is the increased speed, not the original.
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