Question
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You invested \( \$ 12,000 \) in two accounts paying \( 6 \% \) and \( 9 \% \) annual interest, respectively. If the total interest earned for the year was \( \$ 780 \), how much was invested at each rate? The amount invested at \( 6 \% \) is \( \$ \square \). The amount invested at \( 9 \% \) is \( \$ \square \).

Ask by Lewis Marshall. in the United States
Mar 09,2025

Upstudy AI Solution

Tutor-Verified Answer

Answer

The amount invested at \( 6\% \) is \$10,000, and the amount invested at \( 9\% \) is \$2,000.

Solution

**Step 1:** Let \( x \) be the amount invested at \( 6\% \) and \( y \) be the amount invested at \( 9\% \). **Step 2:** The total investment is given by: \[ x + y = 12000 \] **Step 3:** The total annual interest earned is: \[ 0.06x + 0.09y = 780 \] **Step 4:** Solve the first equation for \( y \): \[ y = 12000 - x \] **Step 5:** Substitute \( y \) into the interest equation: \[ 0.06x + 0.09(12000 - x) = 780 \] **Step 6:** Distribute and simplify: \[ 0.06x + 1080 - 0.09x = 780 \] \[ -0.03x + 1080 = 780 \] **Step 7:** Solve for \( x \): \[ -0.03x = 780 - 1080 = -300 \] \[ x = \frac{-300}{-0.03} = 10000 \] **Step 8:** Find \( y \): \[ y = 12000 - 10000 = 2000 \] Thus, the amount invested at \( 6\% \) is \( \$10000 \) and the amount invested at \( 9\% \) is \( \$2000 \).

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The Deep Dive

To solve this investment problem, you can set up a system of equations. Let \( x \) be the amount invested at \( 6\% \) and \( y \) be the amount invested at \( 9\% \). You know that: 1. \( x + y = 12,000 \) 2. \( 0.06x + 0.09y = 780 \) You can solve this system by substitution or elimination. From the first equation, isolate \( y \): \( y = 12,000 - x \). Now substitute this into the second equation: \( 0.06x + 0.09(12,000 - x) = 780 \). After solving this, you'll find that the amount invested at \( 6\% \) is \( \$ 6,000 \) and the amount invested at \( 9\% \) is \( \$ 6,000 \). Remember, keeping track of your variables can make or break your success in these kinds of problems! Ensure you double-check your equations for accuracy. For any future investments, consider diversifying between accounts with differing interest rates. This not only mitigates risk but often maximizes return! A little research on the best compounding interest methods can go a long way too.

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