Question 806673
Let {{{ a }}} = amount invested @ 5%
Let {{{ b }}} = amount invested @ 7% 
Let {{{ c }}} = amount invested @ 10%
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(1) {{{ a + b + c = 20000 }}}
(2) {{{ .05a + .07b + .1c = 1390 }}}
(3) {{{ a = c + 3000 }}}
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You have 3 equations and 3 unknowns,
so it is solvable