Question 615921
Let {{{ j }}} = jt's age
Let {{{ s }}} = sister's age
given:
(1) {{{ s + j = 20 }}}
(2) {{{ j = 2s + 5 }}}
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(1) {{{ s + j = 20 }}}
(2) {{{ 2s - j = -5 }}}
Add the equations
{{{ 3s = 15 }}}
{{{ s = 5 }}}
and, since
(1) {{{ s + j = 20 }}}
(1) {{{ 5 + j = 20 }}}
(1) {{{ j = 15 }}}
JT is 15 and his sister is 5