RRB NTPC · Question 26
A number series is given below with one number missing, shown by a "?". Choose from the options the correct alternative that will fit the pattern of the series. 4, 9, 19, ?, 79, 159
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Answer: (C) 39
Explanation
Each term is double the previous plus 1: 4 → 9 → 19 → 39 → 79 → 159.