Question 618965
Let {{{ j }}} = John's age now
Let {{{ s }}} = Sally's age now
{{{ j + 10 }}} = John's age in 10 years
{{{ s + 10 }}} = Sally's age in 10 years
given:
(1) {{{ j = 7s }}}
(2) {{{ j + 10 + s + 10 = 71 }}}
----------------------
(2) {{{ j + s = 71 - 20 }}}
(2) {{{ j + s = 51 }}}
Substitute (1) into (2)
(2) {{{ 7s + s = 51 }}}
(2) {{{ 8s = 51 }}}
(2) {{{ s = 6.375 }}}
and
(1) {{{ j = 7*6.375 }}}
(1) {{{ j = 44.625 }}}
Note that {{{ .625*12 = 7.5 }}}
John is 44 years and 7 and 1/2 months old
check answer:
(2) {{{ j + s = 51 }}}
(2) {{{ 44.625 + 6.375 = 51 }}}
(2) {{{ 51 = 51 }}}
and
(1) {{{ j = 7s }}}
(1) {{{ 44.625 = 7*6.375 }}}
(1) {{{ 44.625 = 44.625 }}}
OK