Question 1025047
Let {{{ a }}} = number of blue notebooks
Let {{{ b }}} = number of red notebooks
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(1) {{{ a + b = 48 }}}
(2) {{{ a = 2b - 12 }}}
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Substitute (2) into (1)
(1) {{{ 2b - 12 + b = 48 }}}
(1) {{{ 3b = 60 }}}
(1) {{{ b = 20 }}}
and
(2) {{{ a = 2b - 12 }}}
(2) {{{ a = 2*20- 12 }}}
(2) {{{ a = 40 - 12 }}}
(2) {{{ a = 28 }}}
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There are 28 blue notebooks
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check:
(2) {{{ a = 2b - 12 }}}
(2) {{{ 28 = 2*20 - 12 }}}
(2) {{{ 28 = 40 - 12 }}}
(2) {{{ 28 = 28 }}}
OK