Question 1019975
Let {{{ a }}} = the cost of one donut
Let {{{ b }}} = the cost of one large coffee
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(1) {{{ 3a + 2b = 394 }}}
(2) {{{ 2a + 6b = 720 }}} ( in cents )
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Multiply both sides of (1) by {{{ 3 }}} and
subtract (2) from (1)
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(1) {{{ 9a + 6b = 1182 }}}
(2) {{{ -2a - 6b = -720 }}}
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{{{ 7a = 462 }}}
{{{ a = 66 }}}
and
(1) {{{ 3a + 2b = 394 }}}
(1) {{{ 3*66 + 2b = 394 }}}
(1) {{{ 198 + 2b = 394 }}}
(1) {{{ 2b = 196 }}}
(1) {{{ b = 98 }}}
the cost of one donut is $.66
the cost of one large coffee is $.98
check:
(2) {{{ 2a + 6b = 720 }}}
(2) {{{ a + 3b = 360 }}}
(2) {{{ 66 + 3*98 = 360 }}}
(2) {{{ 66 + 294 = 360 }}}
(2) {{{ 360 = 360 }}}
OK