Question 1080946
What they ordered is {{{ 2*pi*r }}} ft of fencing
where {{{ r }}} is the radius of the pool
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What they actually needed was {{{ 2*pi*( r + 4 ) }}} 
ft of fencing
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The extra fencing they need to order is:
{{{ 2*pi*( r+4 ) - 2*pi*r }}}
{{{ 2*pi*r + 8*pi - 2*pi*r }}}
{{{ 8*pi }}}
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They need to order about 25.1327 more feet of fencing
This is about 25' 1.6"
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This says that it doesn't matter how big the pool is, the
extra fencing needed is always the same!
Get a 2nd opinion if needed