due to a problem of my mouse or my browser two threads are being posted for a single topic.....
so i am posting another doubt from binomial....so that the thread does not go into waste...[2][2]
The Value of
\sum_{r=0}^{n} \sum_{s=1}^{n} nCs sCr is
r ≤ s
a)3n - 1 b)3n + 1 c)3n d)N.O.T
answer is a