\(\sum_{r=0}^{n}{}^{n}C_r{}^{r}C_2\) का combinatorial अर्थ क्या है?
What is the combinatorial meaning of \(\sum_{r=0}^{n}{}^{n}C_r{}^{r}C_2\)?
Explanation opens after your attempt
B. एक subset चुनकर उसमें unordered marked pair चुननाChoosing a subset and selecting an unordered marked pair inside it
Concept
Choose the marked pair first and choose the remaining elements freely. In exams think of pair marking when \({}^{r}C_2\) appears.
Why this answer is correct
The correct answer is B. एक subset चुनकर उसमें unordered marked pair चुनना / Choosing a subset and selecting an unordered marked pair inside it. Choose the marked pair first and choose the remaining elements freely. In exams think of pair marking when \({}^{r}C_2\) appears.
Exam Tip
पहले marked pair चुनें और बाकी elements freely choose करें। परीक्षा में \({}^{r}C_2\) दिखे तो pair marking सोचें।
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