Point X and Y are 90 km apart from each other on a highway. A car starts from…
2016
Point X and Y are 90 km apart from each other on a highway. A car starts from X and another from Y at the same time. If they go in the same direction they meet in 9 hours and if they go in opposite directions they meet in 9/7 hours. The maximum speed of the car among the two is:
- A.
20 km/hr
- B.
30 km/hr
- C.
40 km/hr
- D.
50 km/hr
Attempted by 26 students.
Show answer & explanation
Correct answer: C
Let the two speeds be u and v with u ≥ v.
Same direction (they meet in 9 hours): The relative speed is u − v, so u − v = 90 / 9 = 10 km/hr.
Opposite directions (they meet in 9/7 hours): The relative speed is u + v, so u + v = 90 / (9/7) = 70 km/hr.
u − v = 10
u + v = 70
Add the two equations: 2u = 80 ⇒ u = 40 km/hr.
Answer: The maximum speed is 40 km/hr.