Question 679898
Let {{{ a }}} = amount invested at 6%
Let {{{ b }}} = amount invested at 10%
given:
(1) {{{ a + b = 7000 }}}
(2) {{{ .06a + .1b = 900 }}}
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(2) {{{ 6a + 10b = 90000 }}}
Multiply both sides of (1) by {{{ 6 }}}
and subtract (1) from (2)
(2) {{{ 6a + 10b = 90000 }}}
(1) {{{ -6a - 6b = -42000 }}}
{{{ 4b = 48000 }}}
{{{ b = 12000 }}}
and
(1) {{{ a + 12000 = 7000 }}}
(1) {{{ a = -5000 }}}
It is impossible. 
Even if the investor got 10% from both accounts,
the interest would only be $700