A person covers 100 km with a speed of 60 km/h and next 150 km with a speed of…
2019
A person covers 100 km with a speed of 60 km/h and next 150 km with a speed of x km/h. If his average speed for the whole journey is 50 km/h, what is the value of x?
- A.
42
- B.
43
- C.
44
- D.
45
Attempted by 71 students.
Show answer & explanation
Correct answer: D
Total distance = 100 + 150 = 250 km.
Average speed = total distance / total time = 50 km/h → total time = 250 / 50 = 5 hours.
Time for first part = 100 / 60 = 5/3 hours. Time for second part = 150 / x.
So: 5/3 + 150/x = 5 → 150/x = 5 − 5/3 = 10/3.
Therefore x = 150 / (10/3) = 150 * 3 / 10 = 45 km/h.