Binomial Mgf
1. The problem is to find the moment generating function (MGF) of the binomial probability distribution.
2. The binomial distribution models the number of successes in $n$ independent Bernoulli trials, each with success probability $p$.
3. The probability mass function (PMF) of a binomial random variable $X$ is:
$$P(X=k) = \binom{n}{k} p^k (1-p)^{n-k}$$
where $k = 0, 1, 2, \ldots, n$.
4. The moment generating function $M_X(t)$ is defined as:
$$M_X(t) = E[e^{tX}] = \sum_{k=0}^n e^{tk} P(X=k)$$
5. Substitute the PMF into the MGF:
$$M_X(t) = \sum_{k=0}^n e^{tk} \binom{n}{k} p^k (1-p)^{n-k}$$
6. Factor the sum recognizing it as a binomial expansion:
$$M_X(t) = \sum_{k=0}^n \binom{n}{k} (p e^t)^k (1-p)^{n-k} = (p e^t + 1 - p)^n$$
7. Therefore, the moment generating function of a binomial random variable $X$ with parameters $n$ and $p$ is:
$$\boxed{M_X(t) = (1 - p + p e^t)^n}$$
This function can be used to find moments of the distribution by differentiating with respect to $t$ and evaluating at $t=0$.