Posted by **Sarah** on Wednesday, March 9, 2011 at 9:43pm.

an investment of 72,000 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 third 9%. total interest from the investments was $5640. the interest from the first investment was 3 times the interest from the second. find the amounts of three parts of the investment

- Algebra -
**Henry**, Friday, March 11, 2011 at 10:40pm
$X-in 1st inv.

$Y-in 2nd inv.

$Z-in 3rd inv.

0.08X + 0.06Y + 0.09Z = $5640.

Eq1: 0.08X + 0.06Y + 0.09Z = 5640.

Eq2: X + Y + Z = 72000.

Multiply Eq1 by 100 and Eq2 by -9:

8X + 6Y + 9Z = 564000,

-9X - 9Y - 9Z = - 648000,

Add the Eqs:

-X - 3Y = -84,000,

0.08X = 3*0.06Y,

X = 2.25Y

Substitute 2.25Y for X:

-2.25Y - 3Y = -84000,

-5.25Y = -84000,

Y = $16000.

X = 2.25Y = 2.25 * 16000 = $36,000.

X + Y + Z = $72000,

36000 + 16000 + Z = 72000,

Z = $20,000.

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