Question 1043717
You are given two points on the line:
( 50,3 )
( 54,3.95 )
Let {{{ C = f(n) }}} where {{{ C }}} is cost
and {{{ n }}} is the number of pictures ordered
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Use the general point-slope formula
{{{ ( C - 3 ) / ( n - 50 ) = ( 3.95 - 3 ) / ( 54 - 50 ) }}}
{{{  ( C - 3 ) / ( n - 50 ) = .95 / 4 }}}
Multiply both soides by {{{ 4*( n - 50 ) }}}
{{{ 4*( C - 3 ) = .95*( n - 50 ) }}}
{{{ 4C - 12 = .95n - 47.5 }}}
{{{ 4C = .95n - 35.5 }}}
{{{ C = .2375n - 8.875 }}}
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check:
( 50,3 )
{{{ C = .2375n - 8.875 }}}
{{{ 3 = .2375*50 - 8.875 }}}
{{{ 3 = 11.875 - 8.875 }}}
{{{ 3 = 3 }}}
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( 54, 3.95 )
{{{ C = .2375n - 8.875 }}}
{{{ 3.95 = .2375*54 - 8.875 }}}
{{{ 3.95 = 12.825 - 8.875 }}}
{{{ 3.95 = 3.95 }}}
OK