Question 796970
Let {{{ a }}} = Sophie's age now
Let {{{ b }}} = her sister's age now
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(1) {{{ a - 4 = 2*( b - 4 ) }}}
(2) {{{ a = (3/2)*b }}}
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Substitute (2) into (1)
(1) {{{ (3/2)*b - 4 = 2*( b - 4 ) }}}
(1) {{{ (3/2)*b - 4 = 2b - 8 }}}
(1) {{{ 3b - 8 = 4b - 16 }}}
(1) {{{ b = 16 - 8 }}}
(1) {{{ b = 8 }}}
and
(2) {{{ a = (3/2)*8 }}}
(2) {{{ a = 12 }}}
Sophie is 12 now
check:
(1) {{{ a - 4 = 2*( b - 4 ) }}}
(1) {{{ 12 - 4 = 2*( 8 - 4 ) }}}
(1) {{{ 8 = 2*4 }}}
(1) {{{ 8 = 8 }}}
OK