Question 431139
Let {{{t}}} = Tom's age now
Let {{{j}}} = Jerry's age now
given:
(1) {{{ t = j + 4 }}}
(2) {{{ j + 2 = (1/2)*(t + 2) }}}
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(2) {{{2*( j + 2 ) = t + 2 }}}
(2) {{{ 2j + 4 = t + 2 }}}
(2) {{{ t - 2j = 2 }}}
and
(1) {{{ t - j = 4 }}}
Multiply both sides of (1) by {{{2}}}
and subtract (2) from (1)
(1) {{{ 2t - 2j = 8 }}}
(2) {{{ -t + 2j = -2 }}}
{{{ t = 6 }}}
Plug this into (1)
(1) {{{ 6 - j = 4 }}} 
{{{ -j = -2 }}}
{{{ j = 2 }}}
Tom is 6 and Jerry is 2
check:
(1) {{{ t = j + 4 }}}
(1) {{{6 = 2 + 4}}}
OK
(2) {{{ j + 2 = (1/2)*(t + 2) }}} 
(2) {{{ 2 + 2 = (1/2)*(6 + 2) }}} 
(2) {{{ 4 = (1/2)*8 }}}
(2) {{{ 8 = 8 }}}
OK