2016 · Q39
A passenger train takes 1 hour less for a journey of 120 km, if its speed is increased by 10 km/hour from its usual speed. What is its usual speed?
Elementary MathematicsTime, Speed and Distance
- A50 km/hour
- B40 km/hour
- C35 km/hour
- D30 km/hour
Explanation
120/v − 120/(v+10) = 1 gives 1200 = v(v+10), i.e. v²+10v−1200 = 0. The positive root is v = 30 km/h, option D.