Precalc
posted by Kai on .
An investment of $37,000 was made by a business club. The investment was split into three parts and lasted for one year. The first part of the investment earned 8% interest, the second 6%, and the the third 9%. Total interest from the investments was $3030. The interest from the first investment was 6 times the interest from the second. Find the amounts of the three parts of the investment.

amount invested at 8%  x
amount invested at 6%  y
amount invested at 9%  37000xy
.08x + .06y + .09(37000xy) = 3030
times 100
8x + 6y + 9(37000xy) = 303000
x  3y = 30000
x + 3y = 30000 (#1)
also .08x = 6(.06)y
8x = 36y
2x = 9y
x = 9y/2 (#2)
sub into #1
9y/2 + 3y = 30000
times 2
9y + 6y = 60000
y = 4000
then x = 9(4000)/2 = 18000
and 37000400018000 = 15000
$18000 at 8%
$4000 at 6%
$15000 at 9% 
Got it before I saw this xD thanks