Question 656137
Let {{{ a }}} = cost of an adult ticket
Let {{{ c }}} = cost of a child's ticket
given:
(1) {{{ a = 2c }}}
(2) {{{ 3a + 4c = 40 }}}
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Substitute (1) into (2)
(2) {{{ 3*(2c) + 4c = 40 }}}
(2) {{{ 6c + 4c = 40 }}}
(2) {{{ 10c = 40 }}}
(2) {{{ c =4 }}}
and
(1) {{{ a = 2c }}}
(1) {{{ a = 2*4 }}}
(1) {{{ a = 8 }}}
$8 = cost of an adult ticket
$4 = cost of a child's ticket
check:
(2) {{{ 3a + 4c = 40 }}}
(2) {{{ 3*8 + 4*4 = 40 }}}
(2) {{{ 24 + 16 = 40 }}}
(2) {{{ 40 = 40 }}}
OK