Verifying Subtraction Statements

A subtraction statement, like \( 15 - 6 = 9 \), makes a claim: it says that if you take 6 away from 15, you get 9. To verify a subtraction statement means to check whether that claim is actually true. Sometimes a subtraction statement is written correctly, and sometimes it has a mistake, maybe the wrong difference, or the wrong starting number. Learning to verify subtraction statements helps you catch these mistakes and builds a much stronger sense of how numbers up to 20 fit together.

Before working through this lesson, it helps to already be comfortable with basic subtraction facts up to 20, since checking a statement is much easier when you already know several facts by heart.

Every subtraction statement has a matching addition statement. If \( a - b = c \) is true, then adding the part you took away back to the difference should return the original number: \( c + b = a \). This is the fastest and most reliable way to verify a subtraction statement.

For example, to check \( 12 - 5 = 7 \), add the difference and the number subtracted: \( 7 + 5 = 12 \). Since this matches the original number, the subtraction statement is true. If the addition does not match, the subtraction statement is false, and you can then work out the correct answer.

A number line gives a visual way to check the same idea. Start at the first number in the subtraction statement, then count backward by the number being subtracted. If you land exactly on the given difference, the statement is true.

This approach connects closely with skills from using a number line to subtract up to 20, so if the backward jumps feel unfamiliar, it is worth reviewing that method first.

Example 1: Is \( 18 - 9 = 9 \) true or false? Check with addition: \( 9 + 9 = 18 \). Since this matches the first number, the statement is true.

Example 2: Is \( 14 - 5 = 8 \) true or false? Check with addition: \( 8 + 5 = 13 \), not 14. Since this does not match, the statement is false. The correct difference is \( 14 - 5 = 9 \).

Example 3: Is \( 7 - 0 = 7 \) true or false? Check with addition: \( 7 + 0 = 7 \), which matches, so the statement is true. Statements involving zero always follow the same checking rule; you can see more of this idea in subtracting with the number zero.

When you check a subtraction statement, always compare it to a fact you can trust. If addition feels quicker, use the related addition fact. If you prefer a visual approach, use a number line and count the jumps carefully. Either way, focus on one part of the statement at a time: the starting number, the amount subtracted, and the difference, and confirm that all three pieces truly fit together before deciding the statement is correct.

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