A class has n students. We have to form ateam of students including at

1.	A class has n students. We have to form ateam of students including at least 2students and excluding at least 2 students.The number of ways of forming the team is-(A) 2 2n(C) 2'-2n - 4(B) 2" 2n -2(D) of these
Answer» C(n,r)=n!r!(n−r)! ;Required number of ways=nC2+nC3+.......+nCn−3+nCn−2;⇒2n−(nC0+nC1+nCn−1+nCn−1+nCn);⇒2n−2(n+1);⇒2n−2(n+1);⇒2n−2n−2; Correct answer is B thanks

A class has n students. We have to form ateam of students including at least 2students and excluding at least 2 students.The number of ways of forming the team is-(A) 2 2n(C) 2'-2n - 4(B) 2" 2n -2(D) of these

Answer»

C(n,r)=n!r!(n−r)! ;Required number of ways=nC2+nC3+.......+nCn−3+nCn−2;⇒2n−(nC0+nC1+nCn−1+nCn−1+nCn);⇒2n−2(n+1);⇒2n−2(n+1);⇒2n−2n−2;

Correct answer is B

thanks