Chapter 1 - Equations and Inequalities - 1.2 Applications and Modeling with Linear Equations - 1.2 Exercises - Page 103: 37

$\$10,000$ at $2.5\%$ and $\$20,000$ at $3\%$.

Step 1. Assume she deposited $x$ amount at $2.5\%$, thus the amount at $3\%$ would be $2x$ Step 2. The total annual interest can be found as $0.025x+0.03(2x)=850$ Step 3. Solve the equation: $0.085x=850$, thus $x=10,000$ Step 4. Conclusion: deposits $\$10,000$ at $2.5\%$ and $\$20,000$ at $3\%$.