Question 536852
The diameter of the pool is 50 feet.  The walk (circular) around it is 5 feet.  That means there is a circle with 55 feet diameter that isn't grass.<P>
Use pi=22/7.
The radius (r) of a circle is 1/2 the diameter = 1/2 * d.
The area of a circle is {{{A(C) = pi*r^2 = pi*(d/2)^2=(22/7)*(55/2)^2=(22/7)*756.25=2375.8274=2376.79}}}<P>
A(square)=s*s.  <P>
For the given square that's {{{90*90=8100}}}<P>
The grass is the A(square) - A(circle) = 8100-2376.79=5723.21 square feet.<P>
Not sure what the problem indicated you should use as pi.  The answer will be slightly different if 3.14159 is used.

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