Interview Q&A / Aptitude

1. 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
2. What are the fourth proportional, third proportional and mean proportional, with an example of each?

   For a : b = c : d, d is the fourth proportional, d = bc/a (4, 9, 12 gives 27). For a : b = b : c, c is the third proportional, c = b^2/a (4, 6 gives 9). The mean proportional between a and b is the square root of ab (9 and 16 give 12).

   BeginnerQuick answer1 min read