JEE Mains · Maths · STD 11 - 6. permutation and combination
In an examination,\(5\) students have been allotted their seats as per their roll numbers. The number of ways, in which none of the students sits on the allotted seat, is \(..........\).
- A \(43\)
- B \(44\)
- C \(42\)
- D \(41\)
Answer & Solution
Correct Answer
(B) \(44\)
Step-by-step Solution
Detailed explanation
Derangement of \(5\) students \(D_5=5 !\left(1-\frac{1}{1 !}+\frac{1}{2 !}-\frac{1}{3 !}+\frac{1}{4 !}-\frac{1}{5 !}\right)\) \(=120\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{24}-\frac{1}{120}\right)\) \(=60-20+5-1\) \(=40+4\) \(=44\)
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