Question 890285
Let {{{ a }}} = amount invested @ 12%
Let {{{ b }}} = amount invested @ 15%
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(1) {{{ .12a + .15b = 30000 }}}
You are also told that:
(2) {{{ .15a + .12b = 29400 }}}
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(1) {{{ 12a + 15b = 3000000 }}}
(2) {{{ 15a + 12b = 2940000 }}}
Divide both equations by {{{ 3 }}}
(1) {{{ 4a + 5b = 1000000 }}}
(2) {{{ 5a + 4b = 980000 }}}
Multiply both sides of (1) by {{{ 4 }}} and
multiply both sides of (2) by {{{ 5 }}}, then
subtract ( 1) from (2)
(2) {{{ 25a + 20b = 4900000 }}}
(1) {{{ -16a - 20b = 4000000 }}}
{{{ 9a = 900000 }}}
{{{ a = 100000 }}}
and, since
(1) {{{ 4a + 5b = 1000000
(1) {{{ 400000 + 5b = 1000000 }}}
(1) {{{ 5b = 600000 }}}
(1) {{{ b = 120000 }}}
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$100,000 was invested @ 12%
$120,000 was invested @ 15%
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check:
(1) {{{ .12*100000 + .15*120000 = 30000 }}}
(1) {{{ 12000 + 18000 = 30000 }}}
(1) {{{ 30000 = 30000 }}}
OK 
you can check (2)