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
4. If a boy walks to school at 5 km/h he is 7 minutes late; at 6 km/h he is 5 minutes early. How far is the school?

   6 km. The two journey times differ by 7 + 5 = 12 minutes = 1/5 hour. So d/5 - d/6 = 1/5, which gives d/30 = 1/5 and d = 6 km.

   IntermediateQuick answer1 min read
5. In a 1 km race, A beats B by 100 m and B beats C by 100 m. By how many metres does A beat C?

   190 m. When A runs 1,000 m, B runs 900 m. When B runs 1,000 m, C runs 900 m, so when B runs 900 m, C runs 810 m. Hence A beats C by 1,000 - 810 = 190 m.

   IntermediateQuick answer1 min read