Question 1037138
Let {{{ a }}} = man's age now
Let {{{ b }}} = daughter's age now
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(1) {{{ a = 2b }}}
(2) {{{ a - 10 = 3*( b - 10 ) }}}
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Substitute (1) into (2)
(2) {{{ 2b - 10 = 3*( b - 10 ) }}}
(2) {{{ 2b - 10 = 3b - 30 }}}
(2) {{{ b = 20 }}}
The daughter is 20
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check:
(1) {{{ a = 2b }}}
(1) {{{ a = 2*20 }}}
(1) {{{ a = 40 }}}
and
(2) {{{ a - 10 = 3*( b - 10 ) }}}
(2) {{{ a - 10 = 3*( 20 - 10 ) }}}
(2) {{{ a - 10 = 30 }}}
(2) {{{ a = 40 }}}
OK