Question 725879
Let {{{ j }}} = Jane's age now
Let {{{ s }}} = Susan's age now
{{{ j + 20 }}} = Jane's age in 20 years
{{{ s + 20 }}} = Susan's age in 20 years
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given:
(1) {{{ s = 4j + 4 }}}
(2) {{{ j + 20 = (1/2)*( s + 20 ) }}}
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(2) {{{ 2*( j + 20 ) = s + 20 }}}
(2) {{{ 2j + 40 = s + 20 }}}
(2) {{{ s = 2j + 20 }}}
Substitute (1) into (2)
(2) {{{ 4j + 4 = 2j + 20 }}}
(2) {{{ 2j = 16 }}}
(2) {{{ j = 8 }}}
and
(1) {{{ s = 4j + 4 }}}
(1) {{{ s = 4*8 + 4 }}}
(1) {{{ s = 36 }}}
Jane is 8 and Susan is 36
check:
(2) {{{ j + 20 = (1/2)*( s + 20 ) }}}
(2) {{{ 8 + 20 = (1/2)*( 36 + 20 ) }}}
(2) {{{ 28 = 56/2 }}}
(2) {{{ 56 = 56 }}}
OK