Question 553664
Let {{{ r }}} = the cost per gallon of regular
Let {{{ p }}} = the cost per gallon of premium
given:
{{{ 12r }}} = cost of regular used
{{{ 7p }}} = cost of premium used
(1) {{{ 12r + 7p = 48.21 }}}
(2) {{{ p = r + .21 }}}
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Substitute (2) into (1)
(1) {{{ 12r + 7*( r + .21 ) = 48.21 }}}
(1) {{{ 12r + 7r + 1.47 = 48.21 }}}
(1) {{{ 19r = 48.21 - 1.47 }}}
(1) {{{ 19r = 46.74 }}}
(1) {{{ r = 2.46 }}}
and since
(2) {{{ p = r + .21 }}}
(2) {{{ p = 2.67 }}}
Regular is $2.46 per gallon and
premium is $2.67 per gallon
check answer:
(1) {{{ 12*2.46 + 7*2.67 = 48.21 }}}
(1) {{{ 29.52 + 18.69 = 48.21 }}}
(1) {{{ 48.21 = 48.21 }}}
OK