Question 136241
Cost of horse: {{{h}}}
Cost of cow: {{{c}}}
Total cost:  {{{h + c = 800}}}, which can be written: {{{h=800-c}}}


Sell price of horse: {{{h + .1h}}}
Sell price of cow: {{{c - .1c}}}
Total sell price: {{{(h+.1h)+(c-.1c)}}}


Total profit of 2.5% means total sell price of {{{800 + .025*800=820}}}, so:
 

{{{(h+.1h)+(c-.1c)=820}}}
{{{1.1h+.9c=820}}}


But we know that {{{h=800-c}}}, so:
{{{1.1(800-c)+.9c=820}}}


{{{880-1.1c+9c=820}}}
{{{-.2c=-60}}}
{{{c=300}}}


So, the cow cost 300 and the horse cost 500.  The cow sold for 300-30=270, and the horse sold for 500+50=550.  Total revenue:  550+270=820 and 20 is 2.5% profit on 800.  Answer checks.