# Sum of First k binomial coefficients divided by 2^n

I've been solving a complex problem, in which at one step, I have to calculate the following $$\frac {{n \choose 0} + {n\choose 1} + {n\choose 2} + ... + {n\choose k}}{2^n}$$ The values of n and k can be very large $\le 10^5$. But since the answer will always be less than 1 ($k < n$), I was wondering if its calculable doing some modulo trick which will leave me an answer with 4-5 decimal precision.