Grades: 4‒8

In this activity, a continuation of *Mystery Sums Part One*, students use early algebraic reasoning skills to find the numerical values of three variables. Students drag pairs of letters (chosen from *A*, *B*, *–B*, and *C*) across a divider to reveal their sum. With *–B* offered as an addend, students can write equations that include the numerical values of *A* + *B* and *A* – *B*. They can then use algebraic reasoning to find the numerical value of *2A* by adding these two equations together.

OBJECTIVES

- Students will use logical reasoning skills to determine the secret numerical values assigned to variables.
- Students will develop, refine, and share intuitive strategies for solving algebraic equations without formal symbol manipulation.

COMMON CORE CONNECTIONS

Mathematical Practices

(1) Make sense of problems and persevere in solving them; (2) Reason abstractly and quantitatively; (3) Construct viable arguments and critique the reasoning of others; (5) Use appropriate tools strategically; (7) Look for and make use of structure.

Content Standards

6.EE2, 5, 6; 7.EE4; 8.EE8

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