Question 666381
Let {{{ a }}} = number of 20 cent stamps
Let {{{ b }}} = number of 17 cent stamps
given:
(1) {{{ a + b = 100 }}}
(2) {{{ .2a + .17b = 18.83 }}}
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(2) {{{ 20a + 17b = 1883 }}}
Multiply both sides of (1) by {{{ 17 }}}
and subtract (1) from (2)
(2) {{{ 20a + 17b = 1883 }}}
(1) {{{ -17a - 17b = -1700 }}}
{{{ 3a = 183 }}}
{{{ a = 61 }}}
and
(1) {{{ 61 + b = 100 }}}
(1) {{{ b = 100 - 61 }}}
(1) {{{ b = 39 }}}
61 = number of 20 cent stamps
39 = number of 17 cent stamps
check:
(2) {{{ .2*61 + .17*39 = 18.83 }}}
(2) {{{ 12.2 + 6.63 = 18.83 }}}
(2) {{{ 18.83 = 18.83 }}}
OK