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In "Number Series" question, a number series is given with one term missing. Choose the correct alternative that will same pattern and fill in the blank spaces

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

Option:
A. 20
B. 25
C. 30
D. 50
Answer: A . 20

Justification:

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.

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