Find the sum of given series S n = 4 + 44 + 444 + 4444 + ...................n terms Options: A . &nbsp49{109(10(n−1)−1)−n} B . &nbsp49{109(10n−1)−n} C . &nbsp49{10(10n−1)−n} D . &nbsp49{(10n−1)−n}

Find the sum of given series Sn = 4 + 44 + 444 + 4444 + ...................

Question

Find the sum of given series

S_{n}

= 4 + 44 + 444 + 4444 + ...................n terms

Options:

A . 49{109(10(n−1)−1)−n}

B . 49{109(10n−1)−n}

C . 49{10(10n−1)−n}

D . 49{(10n−1)−n}

Answer: Option B
:
B
Reverse Gear Approach
Assume n= 1, then

S_{1}

=4
Now put n=1in options.Eliminate those options , where you are not getting 4.
Only option (b) will give 4.

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