In following number series, two terms have been put within brackets. Choose the appropriate option - Find the wrong number in the series :7, 28, 63, 124, 215, 342, 511

Answer: B. 28

Clearly, the correct sequence is (2^{3} - 1), (3^{3} - 1), (4^{3} - 1), (5^{3} - 1), (6^{3} - 1), (7^{3} - 1), (8^{3} - 1). .'. 28 is wrong and should be replaced by (3^{3} - 1) i.e. 26. Hence, the answer is (b).