Question 1092717
c, cows
r, roosters

{{{c+r=23}}}---------counting heads

{{{4c+2r=72}}}--------counting legs


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Legs equation can be simplified.
{{{2c+r=36}}}


Variable r can be eliminated to first find c.
{{{(2c+r)-(c+r)=36-23}}}
{{{2c-c=13}}}
{{{highlight_green(c=13)}}}-------Number of cows.  Use this to find number of roosters.