problem: While watching a parade I saw some clowns and horses. I counted 30 legs and 10 heads. How many horses did I see in the parade?
solution: Let the number of clowns in the parade be $c$ and the number of horses be $h$. We are looking for the value of $h$. Assuming that each clown has 2 legs and 1 head, and that each horse has 4 legs and 1 head, we can set up the following system of equations:
  
  \begin{align*}
  2c+4h &= 30 \\
  c + h &= 10 \\
  \end{align*}
  
  To solve for $h$, we need to eliminate $c$ from the equations above. We can rewrite the second equation above as $c=10-h$, and substituting this into the first equation to eliminate $c$ gives $2(10-h)+4h = 30$, or $h=5$. Thus, there are $\boxed{5}$ horses in the parade.