Question 1078983
Let {{{ x }}} =the number of doors he painted
that did not need to be repainted
{{{ 25 - x }}} = the number of doors that needed
to be repainted
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{{{ 10x }}} is what he was paid for doors that
did not need repainting
{{{ -5*( 25 - x ) }}} is what he was paid ( fined )
for doors needing repainting
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{{{ 10x - 5*( 25 - x ) = 10 }}}
{{{ 10x - 125 + 5x = 10 }}}
{{{ 15x = 135 }}}
{{{ x = 9 }}}
He painted 9 doors that did not need repainting
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check:
{{{ 10*9 - 5*( 25 - 9 ) = 10 }}}
{{{ 90 - 5*16 = 10 }}}
{{{ 90 - 80 = 10 }}}
{{{ 90 = 90 }}}
OK
You just need to explain {{{ 10x - 5*( 25 - x ) = 10 }}}