Question 937551
Let {{{ w }}} = pints of water needed
{{{ .9*5 = 4.5 }}} pints of developer in 90% solution
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{{{ 4.5 / ( w + 5 ) = .13 }}}
{{{ 4.5 = .13*( w + 5 ) }}}
{{{ 4.5 = .13w + .65 }}}
{{{ .13w = 3.85 }}}
{{{ w = 29.615 }}}
29.615 pints of water should be added
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check:
{{{ 4.5 / ( w + 5 ) = .13 }}}
{{{ 4.5 / ( 29.615 + 5 ) = .13 }}}
{{{ 4.5 = .13*34.615 }}}
{{{ 4.5 = 4.49995 }}}
close enough