find the missing number in the series 84, 81, 88, 14, 12, 18, 9, ?, 11

Question

 i have a question which is troubling me from 2 days, can anyone help me in understanding this question with solution.

Answer 1

The most reasonable answer I can give to this question is 7. Here is the reasoning. Consider 84, 81, 88. The average of 84, and 88 is 86 and 81 is 86-5. Then looking at 14,12,18, the average of 18 and 14 is 16, and 12 is 16-4. Now for 9, ?, 11, the average of 9 and 11 is 10, and you might want to say that the missing number is 10-3 which is 7.

Answer 2

In fact, the correct sequence of the numbers is  84, 14, 12  81, 18, 9 ,88, ?, 11,  

 

If this is the case, the 2nd number = 2(first number/3rd number) 

thus, 84/12 x2 =14 ; 81/9 x2 =18, 88/11  x2= 16

so the answer is 16.