If nPr=nPr+1 and nCr=nCr−1, then the value of n + r is ________.
nPr=nPr+1
or n!(n−r)!=n!(n−r−1)! or n−r=1 (1)
Again nCr=nCr−1=n!(n−r)!r!=n!(n−r+1)!(r−1)!
or 1r=1n−r+1 or n−2r=−1 (2)
Solving (1) and (2), n = 3, r = 2