Question

if n+1C r+1:nCr:n-1Cr-1=8:3:1 find the value of n

Answer 1

Answer :

n=10, r=5

Solution :

Use .nCr.n−1Cr−1=nrand.n+1Cr+1.nCr=n+1r+1.nCr.n-1Cr-1=nrand.n+1Cr+1.nCr=n+1r+1.

∴nr=63=21andn+1r+1=116⇒6n+6=11r+11⇒6n−11r=5∴nr=63=21andn+1r+1=116⇒6n+6=11r+11⇒6n-11r=5.

Solve n-2r=0 and 6n-11r=5.