Question 935846
Let {{{ a }}} = number of 10 cent stamps
Let {{{ b }}} = number of 18 cent stamps
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(1) {{{ a + b = 45 }}}
(2) {{{ 10a + 18b = 666 }}} ( in cents )
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(2) {{{ 5a + 9b = 333 }}}
Multiply both sides of (1) by {{{ 5 }}} and
subtract (1) from (2)
(2) {{{ 5a + 9b = 333 }}}
(1) {{{ -5a - 5b = -225 }}}
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{{{ 4b = 108 }}}
{{{ b = 27 }}}
and
(1) {{{ a + b = 45 }}}
(1) {{{ a + 27 = 45 }}}
(1) {{{ a = 18 }}}
He bought 18 10c stamps