Question 623505
Let {{{ a }}} = amount invested @ 9%
Let {{{ b }}} = amount invested @ 7%
given:
(1) {{{ a + b = 2200 }}}
(2) {{{ .09a + .07b = 160 }}}
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(2) {{{ 9a + 7b = 16000 }}}
Multiply both sides of (1) by {{{ 7 }}}
and subtract (1) from (2)
(2) {{{ 9a + 7b = 16000 }}}
(1) {{{ -7a - 7b = -15400 }}}
{{{ 2a = 600 }}}
{{{ a = 300 }}}
and, since
(1) {{{ a + b = 2200 }}}
(1) {{{ 300 + b = 2200 }}}
(1) {{{ b = 1900 }}}
$300 was invested @ 9%
$1900 was invested @ 7%
check:
(2) {{{ .09a + .07b = 160 }}}
(2) {{{ .09*300 + .07*1900 = 160 }}}
(2) {{{ 27 + 133 = 160 }}}
(2) {{{ 160 = 160 }}}
OK