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

1, ?, 5, 10, 20, 40, 80

Option:
A. 1
B. 2
C. 2.5
D. 4
E. None of these
Answer: D . 4

Justification:

Next number is sum of all previous numbers.

1st Term : 1

2nd Term: 4

3rd Term: 1+4 =5

4th Term: 1+4+5= 10

5th Term: 1+4+5+10=20 and so on....

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