\(\sum_{r=0}^{n}{}^{n}C_r{}^{r}C_k\) का simplified form कौन-सा है?
What is the simplified form of \(\sum_{r=0}^{n}{}^{n}C_r{}^{r}C_k\)?
Explanation opens after your attempt
A. \(^{n}C_k2^{n-k}\)
Concept
Choose the (k) marked members first, then each of the remaining (n-k) members may or may not enter the subset. In exams choose the marked set first in nested selection.
Why this answer is correct
The correct answer is A. \(^{n}C_k2^{n-k}\). Choose the (k) marked members first, then each of the remaining (n-k) members may or may not enter the subset. In exams choose the marked set first in nested selection.
Exam Tip
पहले (k) marked members चुनें, फिर बाकी (n-k) members subset में आएं या न आएं। परीक्षा में nested selection में marked set पहले चुनें।
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