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JEE MATHEMATICS MCQ: PERMUTATIONS

1 Easy

1 of 1

Application +4 | -1

If

a_n=\sum\limits_{{r=0}}^n \frac{1}{{ }^n C_r}

, then

\sum\limits_{{r=0}}^n \frac{r}{{ }^n C_r}

equals:

View answer and explanation

Correct option: A

\frac{n}{2} a_n

Option A (

\frac{n}{2} a_n

) is correct because by using the property

{}^nC_r = {}^nC_{n-r}

, we can rewrite the sum and solve for the desired expression.

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