Question

1) If nC6 = nC4 , then nC2 is
a) 40 b) 45 c)90 d) 50

Answer 1

Step-by-step explanation:

Given

n

C

8

=

n

C

6

⇒

8!(n−8)!

n!

=

6!(n−6)!

n!

⇒

8.7

1

=

(n−6)(n−7)

1

⇒ (n−6)(n−7)=56

⇒ n

2

−13n−14=0

⇒ n=−1 or 14

n cannot be (−)ve, ∴ n=14

Now

n

C

2

=

2!×12!

14!

=

2

14×13

=7×13=91