(\sum_{r=0}^{n}r(r-1){}^{n}C_r) का सही सरल रूप कौन-सा है?
What is the correct simplified form of (\sum_{r=0}^{n}r(r-1){}^{n}C_r)?
Explanation opens after your attempt
Correct Answer
B. (n(n-1)2^{n-2})
Concept
There are (n(n-1)) ways to choose two ordered marked members and the remaining (n-2) are chosen freely. In exams two marks lead to \(2^{n-2}\).
Why this answer is correct
The correct answer is B. (n(n-1)2^{n-2}). There are (n(n-1)) ways to choose two ordered marked members and the remaining (n-2) are chosen freely. In exams two marks lead to \(2^{n-2}\).
Exam Tip
Ordered दो marked members चुनने के (n(n-1)) ways हैं और बाकी (n-2) freely चुने जाते हैं। परीक्षा में दो marks हों तो \(2^{n-2}\) आता है।
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