Question 978701
Let {{{ x }}} = pints of 74% disinfectant needed
{{{ .74x }}} = pints of alcohol in 74% disinfectant
{{{ .9*5 = 4.5 }}} = pints of alcohol in 90% diinfectant
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{{{ ( .74x + 4.5 ) / ( x + 5 ) = .84 }}}
{{{ .74x + 4.5 = .84*( x + 5 ) }}}
{{{ .74x + 4.5 = .84x + 4.2 }}}
{{{ .1x = .3 }}}
{{{ x = 3 }}}
3 pints of 74% disinfectant are needed
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check:
{{{ ( .74x + 4.5 ) / ( x + 5 ) = .84 }}}
{{{ ( .74*3 + 4.5 ) / ( 3 + 5 ) = .84 }}}
{{{ ( 2.22 + 4.5 ) / 8 = .84 }}}
{{{ 6.72 / 8 = .84 }}}
{{{ 6.72 = 6.72 }}}
OK