Ask Questions, Get Answers

Want to ask us a question? Click here
Browse Questions
Home  >>  CBSE XI  >>  Math  >>  Permutations and Combinations
0 votes

A class has 30 students .We have to form a team of the students including atleast two students and also excluding atleast two students.The number of ways of forming the team is

$\begin{array}{1 1}(A)\;2^n-2n\\(B)\;2^n-2n-2\\(C)\;2^n-2n-4\\(D)\;\text{None of these}\end{array} $

Can you answer this question?

1 Answer

0 votes
  • $C(n,r)=\large\frac{n!}{r!(n-r)!}$
Required number of ways=$nC_2+nC_3+.......+nC_{n-3}+nC_{n-2}$
$\Rightarrow 2^n-(nC_0+nC_1+nC_{n-1}+nC_{n-1}+nC_n)$
$\Rightarrow 2^n-2(n+1)$
$\Rightarrow 2^n-2(n+1)$
$\Rightarrow 2^n-2n-2$
Hence (B) is the correct answer.
answered Jun 20, 2014 by sreemathi.v

Related questions

Ask Question
student study plans
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App