Question 838759
There are 3 unknowns, and you can get
3 equations from given data
---------------------------
Let {{{ a }}} = amount invested @ 4%
Let {{{ b }}} = amount invested @ 10%
Let {{{ c }}} = amount invested @ 15%
----------------------------------
(1) {{{ a + b + c = 4950 }}}
(2) {{{ .04a + .1b + .15c = 520 }}}
(3) {{{ b = 2c }}}
-------------------------------
(2) {{{ 4a + 10b + 15c = 52000 }}}
and
Multiply both sides of (1) by {{{ 4 }}}
and subtract (1) from (2)
(2) {{{ 4a + 10b + 15c = 52000 }}}
(1) {{{ -4a - 4b - 4c = -19800 }}}
{{{ 6b + 11c = 32200 }}}
Substitute (3) into this result
{{{ 6*(2c) + 11c = 32200 }}}
{{{ 23c = 32200 }}}
{{{ c = 1400 }}}
and, since
(3) {{{ b = 2c }}}
(3) {{{ b = 2800 }}}
and
(1) {{{ a + b + c = 4950 }}}
(1) {{{ a + 2800 + 1400 = 4950 }}}
(1) {{{ a + 4200 = 4950 }}}
(1) {{{ a = 750 }}}
-----------------
$750 is invested @ 4%
$2800 is invested @ 10%
$1400 is invested @ 15%
----------------------
check:
(2) {{{ .04a + .1b + .15c = 520 }}}
(2) {{{ .04*750 + .1*2800 + .15*1400 = 520 }}}
(2) {{{ 30 + 280 + 210 = 520 }}}
(2) {{{ 520 = 520 }}}
OK