Find the wrong number in the following series.
9, 15, 24, 34, 51, 69

Correct option is B

The series should follow this pattern, (the gape between difference is 3 or we can say double difference is 3)
9 + 6 = 15
15 + 9 = 24
24 + 12 = 36 not 34
36 + 15 = 51
51 + 18 = 69
Hence 34 is correct answer.