Three coins are flipped. Let $X = \text{the number of heads}$.

1. List all of the possible heads/tails combinations of outcomes.

   Hint (a):

   HHH, HHT, ...
   There are eight possible combinations of outcomes.

2. Create a probability model for this situation.

   Hint (b):

   $X$	$0$	$1$	$2$	$3$
   $P(X)$

3. Calculate the expected value of $X$.

   Hint (c):

   $E(x)=\displaystyle \sum _ { } ^ { }X \cdot P(X)$