How can I calculate this summation? $\sum_{x=60}^{100} {100\choose x} $? How can I calculate this summation?
$$\sum_{x=60}^{100} {100\choose x} $$ ?
I don't have idea how to calculate it, I tried to arrive at a probability expression of a random variable that is binomial ($Bin(n,p)$) but But I did not succeed.

$$ \sum_{x=0}^{100} {100 \choose x} = {(2)}^{100} $$
And using the fact that $ {n \choose r} = {n \choose n-r} $ it can be shown that $$ \sum_{x=50}^{100} {100 \choose x} = {(2)}^{99} $$ 
So $$ \sum_{x=60}^{100} {100 \choose x} = {(2)}^{99} - \sum_{x=50}^{59} {100 \choose x} $$
