Look at this series: 80, 10, 70, 15, 60, . . . What number should come next? - Number Series - Serie

In following number series, two terms have been put within brackets. Choose the appropriate option - Look at this series: 80, 10, 70, 15, 60, . . . What number should come next?

A. 20

B. 25

C. 30

D. 50

E. None of the above

Answer: A. 20

This is an alternating addition and subtraction series.
In the first pattern, 10 is subtracted from each number to arrive at the next.
In the second, 5 is added to each number to arrive at the next.

First pattern (80) (80 - 10 = 70) (70 - 10 = 60) (60 - 10 = 50)
Second pattern (10) (10 + 5 = 15) (15 + 5 = 20)
So the answer is a = 20.

Posted in: Number Series - Series Completion - Verbal Reasoning