Multiple choice

A person goes from point N to P and comes back. His average speed for the whole journey is 60 km/hr. If his speed while going from N to P is 40 km/hr, then what will be the speed of the person (in km/hr) while coming back from P to N?

  1. 80

  2. 100

  3. 120

  4. 140
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Average speed = 2xy / (x+y), where x and y are the speeds for the two legs. 60 = 2 * 40 * y / (40 + y). 60(40 + y) = 80y. 2400 + 60y = 80y. 20y = 2400, so y = 120.

AI explanation

Because the distance for both parts of the journey is the same, we use the harmonic mean formula for equal distances: average speed equals (2 times speed 1 times speed 2) divided by (speed 1 plus speed 2). Substituting the known values gives 60 = (2 times 40 times v) divided by (40 + v). Simplifying this yields 2400 + 60v = 80v, so 20v = 2400. Solving for v gives a return speed of 120 km/hr.

Keep practicing — related questions