# Math Help - even and odd probability of coin

1. ## even and odd probability of coin

hi,
i am preparing for an exam and i wondered if some one could show me explicitly
how to calculate the probability of getting an even number of heads in flipping a coin, with probability p for heads n times.
i know i need to sum a series but i can't manage to do it well.
something that doesn't use too advanced math.

n=number of throws....

the probability of getting an even number of heads can be expressed
by expanding the binomial,
or logically as follows....

$=(1-p)^n+\binom{n}{2}p^2(1-p)^{n-2}+\binom{n}{4}p^4(1-p)^{n-4}+......$