Question 1210285
<pre>

The 27 animal heads can't be all be chicken heads, for if they were, 
they'd have only 
27x2=54
feet under them. So where did the other 
78-54=24 
feet come from?  
From the 24/2=12 pigs' right and left hind feet.  
So there were 12 pigs and 27-12=15 chickens.

Or, you can solve it this way:

The 27 animal heads can't all be pig heads for if they were, they'd have 
27x4=108 
feet under them. So how did the 108 feet get reduced by 108-78=30? 
By the 30/2=15 chicken heads' failure to have a pair of hind feet 
under them.
So there were 15 chickens and 27-15=12 pigs.  

Edwin</pre>