Find the probability distribution of the number of heads in four tosses of a coin.

(N/A) When a coin is tossed four times,the total number of outcomes is $2^4 = 16$. The sample space $S$ is:
$S = \{HHHH, HHHT, HHTH, HHTT, HTHH, HTHT, HTTH, HTTT, THHH, THHT, THTH, THTT, TTHH, TTHT, TTTH, TTTT\}$
Let $X$ be the random variable representing the number of heads. $X$ can take values $0, 1, 2, 3, 4$.
$P(X=0) = P(TTTT) = \frac{1}{16}$
$P(X=1) = P(HTTT) + P(THTT) + P(TTHT) + P(TTTH) = \frac{1}{16} + \frac{1}{16} + \frac{1}{16} + \frac{1}{16} = \frac{4}{16} = \frac{1}{4}$
$P(X=2) = P(HHTT) + P(HTHT) + P(HTTH) + P(THHT) + P(THTH) + P(TTHH) = \frac{6}{16} = \frac{3}{8}$
$P(X=3) = P(HHHT) + P(HHTH) + P(HTHH) + P(THHH) = \frac{4}{16} = \frac{1}{4}$
$P(X=4) = P(HHHH) = \frac{1}{16}$
The probability distribution is:

$X$	$0$	$1$	$2$	$3$	$4$
$P(X)$	$\frac{1}{16}$	$\frac{1}{4}$	$\frac{3}{8}$	$\frac{1}{4}$	$\frac{1}{16}$