Applications of Systems of Linear Equations

Question

Amber invests $800 in one account and $2000 in an account paying 3 % higher interest. At the end of one year she had earned $172 in interest. At what rates did she invest?

Answer 1

Let x be the interest rate on the $800. The interest rate on the $2000 is 3% (0.03) higher, so it's x + 0.03. So we have:

$800x + $2000(x + 0.03) = $172

Solve for x, the interest rate on the $800. The interest rate on the $2000 is x + 0.03. Multiply both by 100 to convert to a %.