Multiple choice

A person travels from A to B at the speed of 120 km an hour and returns from B to A at the speed of 80 - km an hour. What is his average speed?

  1. 100 km/hr

  2. 96 km /hr

  3. 90 km /hr

  4. 60 km /hr

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Average speed for a round trip is calculated as (2 * v1 * v2) / (v1 + v2). Plugging in 120 and 80 gives (2 * 120 * 80) / (120 + 80) = 19200 / 200 = 96 km/hr.

AI explanation

When equal distances are covered at two different speeds, the average speed is calculated using the harmonic mean formula: 2xy / (x + y). Substituting the given speeds of 120 km/hr and 80 km/hr gives (2 * 120 * 80) / (120 + 80). This evaluates to 19200 / 200, which results in an average speed of 96 km/hr.