Skill: Use a symbol for an unknown

Explanation and Free Practice Resources

A symbol or letter can represent an unknown whole number in an equation, and its value is determined by the relationship that makes the equation true, including cases where the unknown appears before or after an operation (for example, □ + 8 = 15 or 4 × n = 20). This understanding treats the equal sign as a statement of equivalence and does not extend to formal algebraic manipulation, negative numbers, or generalized equations.

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Detailed Explanation: Use a symbol for an unknown

A symbol, such as $\square$ or $n$ , can stand for a number we do not know yet. The equal sign means both sides have the same value.

Example:

4 \times n = 20

The equation says that $4$ groups of the same number make $20$ .
Think: What number multiplied by $4$ equals $20$ ?
Since $4 \times 5 = 20$ , the unknown number is $5$ .
Check the equation:

4 \times 5 = 20

So, $n = 5$ .

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