Quantities that change together

Japanese school year: Elementary 4

What you learn

Learn how to observe how one quantity changes as another changes by organizing data into tables. This foundational skill helps students discover mathematical rules and prepare for studying functions. Prior ability to read tables and perform basic arithmetic is recommended.

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Key points

This method is used to investigate the relationship between two interrelated quantities. Organizing values into a table makes it easy to identify rules and patterns in how one value changes as the other increases.

This formula expresses a relationship where the sum of two quantities, $x$ and $y$ , is always a fixed constant $k$ . Because the total is fixed, $y$ decreases by the exact amount that $x$ increases.

x + y = k

This formula represents a relationship where the difference between two quantities, $y$ and $x$ , remains a constant value $k$ , like an age difference. Because both quantities change by the same amount, their difference never changes.

y - x = k

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Practice 1Coming soon