2020 · Q29
A train takes two hours less for a journey of 300 km if its speed is increased by 5 km/hr from its usual speed. What is its usual speed?
Elementary MathematicsTime, Speed and Distance
- A50 km/hr
- B40 km/hr
- C35 km/hr
- D25 km/hr
Explanation
300/u − 300/(u + 5) = 2 gives 1500 = 2u(u + 5), i.e. u² + 5u − 750 = 0. Factorising: (u + 30)(u − 25) = 0, so the (positive) speed is 25 km/hr.