Formulas: Financial Concepts [TEKS Tools Grade 8]

This post specifically looks at how formulas can be used solve problems involving simple and compound interest. Read more about TEKS Tools and their rationale here.

Formulas

Formulas account for around 38% of each 8th grade STAAR test. These formulas are applied to solve problems related to volume, surface area, triangles, similar shapes, linear relationships, and finances.

The main function of a formula is to understand the relationship between quantities. In fourth grade, students were first introduced to the formulas for area and perimeter of squares and rectangles. In fifth grade, they were introduced to the formula for volume of a rectangular prism. In sixth grade, the formulas for area of a triangle, parallelogram, and trapezoid are explored. In 7th grade, students are introduced to surface area and to circle geometry, exploring π (pi), circumference, and area. Now in 8th grade, students stabilize their previous learning about linear relationships, surface area, volume (including composite shapes), and finances while beginning to explore geometric concepts such as the Pythagorean Theorem.

Interest

Students continue their use of simple and compound interest formulas to solve problems.

8.12A - solve real-world problems comparing how interest rate and loan length affect the cost of credit

2025-34: an amount and two simple interest rates were given, students had to compare the two

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8.12C - explain how small amounts of money invested regularly, including money saved for college and retirement, grow over time

2024-7: an investment account with simple interest was given, students had to describe the yearly changes

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8.12D - calculate and compare simple interest and compound interest earnings

2023-17: a principal and simple interest rate were given, students had to calculate the interest earned

2023-37: a principal and compound interest rate were given, students had to calculate the interest earned

2024-16: a principal, simple interest rate, and compound interest rate were given, students had to compare the two balances

2024-24: a principal and simple interest rate were given, students had to calculate the interest earned

2025-2: a principal and simple interest rate were given, students had to calculate the interest earned and new balance

2025-26: a principal, simple interest rate, and compound interest rate were given, students had to compare the two balances