Question 1063210
Let {{{ a }}} = the cost of a half dozen cookies
{{{ 2a }}} = the cost of a dozen cookies
Let {{{ b }}} = the cost of a loaf of bread
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(1) {{{ 2a + b = 670 }}} ( in cents )
(2) {{{ a + 2b = 605 }}} ( in cents )
Multiply both sides of (2) by {{{ 2 }}} and
subtract (1) from (2)
(2) {{{ 2a + 4b = 1210 }}}
(1) {{{ -2a - b = -670 }}}
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{{{ 3b = 540 }}}
{{{ b = 180 }}} cents
A loaf of bread costs $1.80
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check:
(1) {{{ 2a + b = 670 }}} 
(1) {{{ 2a + 180 = 670 }}} 
(1) {{{ 2a = 490 }}}
(1) {{{ a = 245 }}}
and
(2) {{{ a + 2b = 605 }}}
(2) {{{ 245 + 2*180 = 605 }}}
(2) {{{ 245 + 360 = 605 }}}
(2) {{{ 605 = 605 }}}
OK