2023 · Q42
Car A takes 1 hour more than car B, which travels at a speed of 60 km per hour, to cover some fixed distance. If car A had doubled its speed, it could cover the distance in 1 hour less time than car B travelling at 60 km per hour. What is the original speed of car A in km per hour?
general-mental-abilityquantitative-aptitude
- A30
- B40
- C45
- D50
Explanation
Let car B's time be t hours, so the distance is 60t km. Car A takes t+1 hours, giving A's speed as 60t/(t+1). Doubling A's speed halves its time to (t+1)/2, which equals one hour less than B's time, i.e. t-1. Solving (t+1)/2 = t-1 gives t = 3, so the distance is 180 km and A's original speed is 180/4 = 45 km/h. Hence option C.