JEE Math Practice Question
The sum $$\sum\limits_{k = 1}^{20} {k{1 \over {{2^k}}}} $$ is equal to
- A.$$2 - {11 \over {{2^{19}}}}$$
- B.$$2 - {3 \over {{2^{17}}}}$$
- C.$$1 - {11 \over {{2^{20}}}}$$
- D.$$2 - {21 \over {{2^{20}}}}$$
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