What number should replace the question mark in this sequence? 6; 11; 9; 14; 12; 17; 15; ?; 18

Question

What number should replace the question mark?

12 - - - 25

5 - - - 11

21 - - - 43

18 - - - 37

2 - - - ?

Answer 1

20

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6; 11; 9; 14; 12; 17; 15; 20; 18
there are 2 series in one with the increment of 3:
6-9-12-15-18
11-14-17-20

Answer 2

20... as once you add 5 to the prev number and then sub 2

Answer 3

20 is the answer. The pattern is +5, -2.