Question 984892
The person has bought {{{ 1 }}} 
gallon for price {{{ p }}}
The price for the {{{ 1 }}} gallon 
goes up to {{{ 1.2p }}}
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Let {{{ x }}} = the number of gallons he needs to buy
The person wants to pay {{{ 1.08p }}}
The price/gal is {{{ 1.2p/1 }}}
[ price/gal ]x[ gal ] = [ price ]
{{{ 1.2p*x = 1.08p }}}
{{{ x = 1.08/1.2 }}}
{{{ x = .9 }}}
{{{ 1 - .9 = .1 }}}
{{{ .1*100 = 10 }}}
He must buy 10% less gasoline
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check:
{{{ .9*1.2 = 1.08 }}} 
OK