Multiple choice

The summation of series S = $2 + \frac{5}{2} + \frac{8}{2^2} + \frac{11}{2^3} + ..... \propto$ is

  1. 4.50

  2. 6.0

  3. 6.75

  4. 10.0
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D Correct answer
Explanation

This is an arithmetico-geometric series: S = 2 + 5/2 + 8/4 + 11/8 + ... The sum of an infinite AGP is S = a/(1-r) + dr/(1-r)^2, where a=2, d=3, r=1/2. S = 2/(0.5) + (3*0.5)/(0.5^2) = 4 + 1.5/0.25 = 4 + 6 = 10.

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