Question 597990
Let {{{ a }}} = number of 50 cent notepads ordered
Let {{{ b }}} = number of 70 cent notepads ordered
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given:
(1) {{{ a + b = 550 }}}
(2) {{{ .5a + .7b = 311 }}}
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(2) {{{ 5a + 7b = 3110 }}}
Multiply both sides of (1) by {{{5}}}
and subtract (1) from (2)
(2) {{{ 5a + 7b = 3110 }}}
(1) {{{ -5a - 5b = -2750 }}}
{{{ 2b = 360 }}}
{{{ b = 180 }}}
and, since
(1) {{{ a + b = 550 }}}
(1) {{{ a + 180 = 550 }}}
(1) {{{ a = 370 }}}
370 50 cent notepads were ordered
180 70 cent notepads were ordered
check:
(2) {{{ .5a + .7b = 311 }}}
(2) {{{ .5*370 + .7*180 = 311 }}}
(2) {{{ 185 + 126 = 311 }}}
{2) {{{ 311 = 311 }}}
OK