EduGoog
In following number series, two terms have been put within brackets. Choose the appropriate option

Look at this series: 53, 53, 40, 40, 27, 27, . . .What number should come next ?

Option:
A. 12
B. 14
C. 27
D. 53
Answer: B . 14

Justification:

In this series, each number is repeated, then 13 is subtracted to arrive at the next number.
Rule = (1st number) (1st number) (1st number - 13 = 2nd number) (2nd number repeat) (2nd - 13 = 3rd number) (3rd number repeat)....
The series is 53, 53, 40, 40, 27, 27...
(53),(53 - 13 = 40), (40), (40 - 13 = 27) (27), (27 - 13 = 14), (14)...
So the answer is b = 14. 

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