What is the average speed if a person travels from A to B and then B to C at…
2025
What is the average speed if a person travels from A to B and then B to C at the speeds of 10 km/hr and 20 km/hr, respectively for equal intervals of time?
- A.
15 kmph
- B.
13.33 kmph
- C.
12 kmph
- D.
11.11 kmph
Attempted by 834 students.
Show answer & explanation
Correct answer: A
Explanation: For equal intervals of time, the average speed is the arithmetic mean of the speeds.
Compute the arithmetic mean:
(10 + 20) / 2 = 15 km/hr
Therefore the average speed is 15 km/hr.
Note: For equal distances (not equal times), the average speed is the harmonic mean. For speeds a and b, harmonic mean = 2ab/(a + b). For 10 and 20 this gives 13.33 km/hr.
Key takeaway: Use the arithmetic mean when time intervals are equal; use the harmonic mean when distances are equal.