Question 1035980
I don't know what the 6-step method is, but
this is how I do it:
Let {{{ x }}} = gallons of 70% antifreeze needed
{{{ .25*90 = 22.5 }}} gallons of pure antifreeze in 25% solution
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{{{ ( .7x + 22.5 ) / ( x + 90 ) = .6 }}}
{{{ .7x + 22.5 = .6*( x + 90 ) }}}
{{{ .7x + 22.5 = .6x + 54 }}}
{{{ .1x = 31.5 }}}
{{{ x = 315 }}}
315 gallons of 70% antifreeze are needed
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check:
{{{ ( .7x + 22.5 ) / ( x + 90 ) = .6 }}}
{{{ ( .7*315 + 22.5 ) / ( 315 + 90 ) = .6 }}}
{{{ ( 220.5 + 22.5 ) / 405 = .6 }}}
{{{ 243 = .6*405 }}}
{{{ 243 = 243 }}}
OK