Question 614316
Let {{{ a }}} = boy's age now
Let {{{ b }}} = Father's age now
given:
(1) {{{ a/b = 1/4 }}}
(2) {{{ ( a + 4 ) / ( b + 4 ) = 1/3 }}}
--------------------------
(1) {{{ 4a = b }}}
By substitution:
(2) {{{ ( a + 4 ) / ( 4a + 4 ) = 1/3 }}}
(2) {{{ 3*( a + 4 ) = 4*( a + 1 ) }}}
(2) {{{ 3a + 12 = 4a + 4 }}}
(2) {{{ a = 8 }}}
and
(1) {{{ a/b = 1/4 }}}
(1) {{{ 8/b = 1/4 }}}
(1) {{{ 32 = b }}}
The boy is 8 now
check:
(2) {{{ ( a + 4 ) / ( b + 4 ) = 1/3 }}}
(2) {{{ ( 8 + 4 ) / ( 32 + 4 ) = 1/3 }}}
(2) {{{ 12 / 36 = 1/3 }}}
(2) {{{ 3*12 = 36 }}}
(2) {{{ 36 = 36 }}}
OK