Find the value of 1000C500+1000C501
nCr+nCr−1=n+1Cr
Here, n=1000 and r=501
⇒1000C500+1000C501=1001C501
Explanation for the result:
nCr+nCr−1=n!(n−r)!×r!+n!(n−(r−1))!×(r−1)!
= n!(n−r)!×(r−1)!(1r+1(n−(r−1)))
= n!(n−r)!×(r−1)!(n−r+1+r)(n−(r−1)×r)
= (n+1)n!(n−r)!×(n−(r−1)(1r(r−1)!)
= (n+1)!(n−r+1)!(1r!)
= n+1Cr