Question 648125
{{{ x }}} = ml of 9% solution needed
{{{ .09x }}} = ml of Minoxidil in 9% solution
{{{ .05*90 = 4.5 }}} ml of Minoxidil in 5% solution
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{{{ ( 4.5 + .09x ) / ( x + 90 ) = .07 }}}
{{{ 4.5 + .09x = .07*( x + 90 ) }}}
{{{ 4.5 + .09x = .07x + 6.3 }}}
{{{ .02x = 6.3 - 4.5}}}
{{{ .02x = 1.8 }}}
{{{ x = 90 }}}
90 ml of 9% solution are needed
check:
{{{ ( 4.5 + .09x ) / ( x + 90 ) = .07 }}}
{{{ ( 4.5 + .09*90 ) / ( 90 + 90 ) = .07 }}}
{{{ ( 4.5 + 8.1 ) / 180 = .07 }}}
{{{ 12.6  = .07*180 }}}
{{{ 12.6 = 12.6 }}}
OK