Question 925988
x, the uniform width around the pool.


{{{(15+2x)(10+2x)-15*10=250}}}; you want the difference in area to be 250 square yards.  Simplify this equation.  


{{{(15+2x)(10+2x)=250+150}}}
{{{15*10+50x+4x^2=250+150}}}
{{{50x+4x^2=250}}}
{{{25x+2x^2=125}}}
{{{2x^2+25x-125=0}}}


You can try to factor, but alternatively, preparing for general solution method,
discriminant is {{{25^2-4*2(-125)=625+8*125=1625=25*65=5*5*5*13}}}.


{{{x=(-25+sqrt(5^3*13))/4}}}


{{{highlight(x=(-25+5*sqrt(65))/4)}}}

About 3.83 yards.
About 3 yards 2 feet 6 inches