Question

nCr-1 = 495
ncr= 220
ncr+1= 66, find rc4​

Answer 1

Answer:

n

C

r

n

C

r−1

=

n−r+1

r

and

n

C

r+1

n

C

r

=

n−r

r+1

∴

n−r+1

r

=

84

36

=

7

3

⇒3n−3r+3=7r⇒3n−10r=−3...(i)

and

n−r

r+1

=

126

84

=

3

2

⇒2n−2r=3r+3⇒2n−5r=3...(ii)

(i)−2×(ii)

3n−10r−4n+10r=−3−6⇒−n=−9⇒

n=9

putting value of n in (i), we get

27+3=10r⇒

r=3

please mark me as the brainliest......