Question 996959
Let {{{ n }}} = number of scoops for both 
ice cream parlor and sundae shop
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This equation makes cost for 1 cone at
both places equal
{{{ 225 + 70*( n-2 ) = 210 + 65*( n-1 ) }}}
{{{ 225 + 70n - 140 = 210 + 65n - 65 }}}
{{{ 5n = 210 - 65 + 140 - 225 }}}
{{{ 5n = 60 }}}
{{{ n = 12 }}}
One more scoop, or 13 scoops
makes the ice cream parlor a better deal
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check:
Making the costs equal:
{{{ 225 + 70*( n-2 ) = 210 + 65*( n-1 ) }}}
{{{ 225 + 70*( 12-2 ) = 210 + 65*( 12-1 ) }}}
{{{ 225 + 70*10 = 210 + 65*11 }}}
{{{ 225 + 700 = 210 + 715 }}}
{{{ 925 = 925 }}}
OK
And if there are 13 scoops:
Sundae shop:
{{{ 225 + 70*( n-2 ) }}}
{{{ 225 + 70*( 13 - 2 ) }}}
{{{ 225 + 70*11 }}}
{{{ 225 + 770 = 995 }}}
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ice cream parlor:
{{{ 210 + 65*( n-1 ) }}}
{{{ 210 + 65*( 13 - 1 ) }}}
{{{ 210 + 65*12 }}}
{{{ 210 + 780 = 990 }}}
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The ice cream parlor is 5 cent cheaper