Question 335897
<pre><b>
It is obvious that they all have to be pigs with no chickens,
since 100=4*25, there are 4 times as many legs as there are heads,
and of course there are 25 pigs and no chickens.  So this is a strange
problem.  I hope the problem didn't state that there had to be some 
chickens, since there aren't any.  But anyway, we'll go through what 
was giving you trouble.

{{{system(x+y=25, 4x+2y=100)}}}

Solve the first equation for either letter.  I will
arbitrarily choose to solve the first equation for y

{{{x+y=25}}}
{{{y=25-x}}}

Next substitute {{{(25-x)}}} for y in the second equation:

{{{4x+2(25-x)=100}}}
{{{4x+50-2x=100}}}
{{{2x+50=100}}}
{{{2x=50}}}
{{{x=25}}}

So since

{{{y=25-x}}}
{{{y=25-25}}}
{{{y=0}}}

So there are 25 pigs and no chickens.

Edwin</pre>