A learner determines an unknown in a whole-number subtraction equation within 1,000 by interpreting the relationship among the minuend, subtrahend, and difference, using inverse addition, related fact families, or a number line or bar model. The reasoning distinguishes cases such as □ − 246 = 517 and 863 − □ = 517 rather than treating subtraction as commutative; negative numbers, decimals, fractions, and general algebraic equations are outside this scope.
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Detailed Explanation: Find a missing number in a subtraction equation
In a subtraction equation, the number being taken away and the answer help you find the missing number.
Example:
The missing number is the minuend, or the starting number. To find it, use the inverse operation: addition.
Add the number taken away to the difference:
So, replace the box with :
Check by subtracting:
Therefore, the missing number is
Remember: when the missing number is the starting number, add the other two numbers.
Learn by doing: Find a missing number in a subtraction equation
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Practice:
Subtraction - Missing Value, 3 Digit, 1 Number
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Download/Modify Free Grade 3 'Find a missing number in a subtraction equation' Worksheet
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This Worksheet Includes:
- Subtraction - Missing Value, 3 Digit, 1 Number
- Subtraction - Missing Value, 2 Digit, 1 Number
- Subtraction - Missing Value, 1 Digit, 1 Number
- Subtraction - Missing Value, Within 20
- Subtraction - Missing Value, From Multiples of Hundreds
- Subtraction - Missing Value, From One Hundred
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