Question 720620
Let {{{ f }}} = Father's age now
Let {{{ s }}} = Son's age now
given:
(1) {{{ f = 4s }}}
(2) {{{ f - 5 = 5*( s - 5 ) }}}
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(2) {{{ f - 5 = 5s - 25 }}}
(2) {{{ 5s - f = 20 }}}
By substitution:
(2) {{{ 5s - 4s = 20 }}}
{{{ s = 20 }}}
and
(1) {{{ f = 4s }}}
(1) {{{ f = 4*20 }}}
(1) {{{ f = 80 }}}
The Father is 80
The Son is 20
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check:
5 years ago, the Father was {{{ 75 }}}
5 years ago, the Son was {{{ 15 }}}
{{{ 75 = 5*15 }}}
{{{ 75 = 75 }}}
OK