Question 1094676
Let {{{ a }}} = father's age now
Let {{{ b }}} = son's age now
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(1) {{{ ( a - 5 ) + ( b - 5 ) = 30 }}}
(2) {{{ a + 5 = 2*( b + 5 ) + 5 }}}
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(1) {{{ a + b - 10 = 30 }}}
(1) {{{ a + b = 40 }}}
and
(2) {{{ a + 5 = 2b + 10 + 5 }}}
(2) {{{ a - 2b = 10 }}}
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Subtract (2) from (1)
(1) {{{ a + b = 40 }}}
(2) {{{ -a + 2b = -10 }}}
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{{{ 3b = 30 }}}
{{{ b = 10 }}}
and
(1) {{{ a + 10 = 40 }}}
(1) {{{ a = 30 }}}
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The father is 30 and the son is 10 
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check:
(2) {{{ a - 2b = 10 }}}
(2) {{{ 30 - 2*10 = 10 }}}
(2) {{{ 30 - 20 = 10 }}}
(2) {{{ 10 = 10 }}}
OK