Interview Q&A / Aptitude

1. A car travels for the first half of the journey's time at 50 km/h and the second half of the time at 70 km/h. What is its average speed?

   60 km/h. When the time intervals are equal, the average speed is the simple average of the speeds: (50 + 70)/2 = 60. For example, 1 hour at 50 and 1 hour at 70 covers 120 km in 2 hours.

   BeginnerQuick answer1 min read
2. A person travels from Pune to Mumbai at 60 km/h and returns at 40 km/h. What is the average speed for the whole trip?

   48 km/h, not 50. For equal distances the average speed is the harmonic mean: 2 x 60 x 40 / (60 + 40) = 4,800 / 100 = 48 km/h, because more time is spent at the slower speed.

   BeginnerQuick answer1 min read
3. Walking at 3/4 of his usual speed, a student reaches college 20 minutes late. What is his usual time for the journey?

   60 minutes. For a fixed distance, time is inversely proportional to speed. At 3/4 speed the time becomes 4/3 of usual, so the extra 1/3 of the usual time equals 20 minutes and the usual time is 60 minutes.

   BeginnerQuick answer1 min read