SOLUTION: Vien invested $880, part at 9% per annum and the rest at 12% per annum. After one year the total interest earned was $79.50. How much did he invest at each rate?

Question 1200564: Vien invested $880, part at 9% per annum and the rest at 12% per annum. After one year the total interest earned was $79.50. How much did he invest at each rate?
Answer by ikleyn(52799) (Show Source): You can put this solution on YOUR website!
.


x dollars invested at 12%;  (880-x) dollars invested at 9%.


Write an equation for total annual interest

    0.12x + 0.09*(880-x) = 79.50  dollars


Simplify and find x

    0.12x + 0.09*880 - 0.09x = 79.50

    0.12x - 0.09x = 79.50 - 0.09*880

        0.03x     =    0.3

            x     =    0.3/0.03 = 10.


ANSWER.  $10 invested at 12%;  880-10 = 870 dollars invested at 9%.


CHECK.  0.12*10 + 0.09*870 = 79.5  dollars.  ! correct !

Solved.

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To see many other similar solved problems using one equation in one unknown, look into the lesson
- Typical investment problems
in this site.

To see many other similar solved problems using systems of two equations in two unknowns, look into the lesson
- Using systems of equations to solve problems on investment
in this site.

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