Question 1087058
Let {{{ g }}} = the girl's age
Let {{{ m }}} = the mother's age
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(1) {{{ g = m - 18 }}}
(2) {{{ ( g + 6 ) + ( m + 6 ) = 54 }}}
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(2) {{{ g + m + 12 = 54 }}}
(2) {{{ g + m = 42 }}}
and
(1) {{{ g - m = -18 }}}
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Add (1) and (2)
(2) {{{ g + m = 42 }}}
(1) {{{ g - m = -18 }}}
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{{{ 2g = 24 }}}
{{{ g = 12 }}}
The girl is 12
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check:
(1) {{{ g = m - 18 }}}
(1) {{{ 12 = m - 18 }}}
(1) {{{ m = 30 }}}
and
(2) {{{ g + m = 42 }}}
(2) {{{ 12 + 30 = 42 }}}
(2) {{{ 42 = 42 }}}
OK