Question 642051
Let {{{ x }}} = Son's age in Jan 2000
Let {{{ y }}} = Lisa's age in 2000
{{{ 11x }}} = Lisa's age in Jan 2000
When Son is {{{ x + 12 }}},
Lisa is {{{ 3*( x + 12 ) }}}
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(1) {{{ y = 11x }}}
(2) {{{ y + 12 = 3*( x + 12 ) }}}
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Substitute (1) into (2)
(2) {{{ 11x + 12 = 3*( x + 12 ) }}}
(2) {{{ 11x + 12 = 3x + 36 }}}
(2) {{{ 11x - 3x = 36 - 12 }}}
(2) {{{ 8x = 24 }}}
(2) {{{ x = 3 }}}
and
(1) {{{ y = 11*3 }}}
(1) {{{ y = 33 }}}
Your Son was 3 in Jan 2000
check:
(2) {{{ y + 12 = 3*( x + 12 ) }}}
(2) {{{ 33 + 12 = 3*( 3 + 12 ) }}}
(2) {{{ 45 = 3*15 }}}
(2) {{{ 45 = 45 }}}
OK