Reasoning - Series Completion - Discussion

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Q.

Which term of the series 5, 10, 20, 40, ..... is 1280?  .                          
A. 10th B. 8th
C. 9th D. None Of These

Answer: Option B
Explaination:

 


Clearly, 5 x 2 = 10, 10 x 2 = 20, 20 x 2 = 40,.....
So, the series is a G.P. in which a = 5 and r = 2.
Let 1280 be the rath term of the series.
Then, 5x2n-1 = 1280 2n-1 = 256 = 28 n - 1 = 8 n = 9.




Discussion

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