Interview Q&A / Aptitude

1. Find the wrong term in the series 3, 7, 15, 27, 63, 127.

   27 is wrong; it should be 31. Each term is double the previous plus 1: 3, 7, 15, 31, 63, 127. Equivalently each term is 2^n - 1.

   BeginnerQuick answer1 min read
2. What is the next letter in the series A, C, F, J, O, ...?

   U. Using positions A = 1, C = 3, F = 6, J = 10, O = 15, the gaps are 2, 3, 4, 5, so the next gap is 6 and the next position is 21, which is U.

   BeginnerQuick answer1 min read
3. What is the next number in the series 2, 3, 5, 9, 17, ...?

   33. The differences are 1, 2, 4, 8, which double each time, so the next difference is 16 and 17 + 16 = 33. Each term is also 2^n + 1, or double the previous term minus 1.

   BeginnerQuick answer1 min read
4. What is the next term in the series 4, 9, 25, 49, 121, ...?

   169. The terms are squares of consecutive prime numbers: 2^2, 3^2, 5^2, 7^2, 11^2, so the next is 13^2 = 169.

   BeginnerQuick answer1 min read