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Definition:
In determining the unknown whole number in an addition and subtraction equation, we must understand the correlation of addition and subtraction as part of a whole.
- The biggest number is called the whole.
- The other two numbers are its parts.
Adding the parts gives the whole.
12 + 6 = 18
6 + 12 = 18
Subtracting one part from the whole gives the other part.
18 – 6 = 12
18 – 12 = 6
Examples:
If the unknown number is the subtrahend, subtract the difference from the minuend (number before the minus sign).
15 – 11 = 4
Therefore, the unknown number is 4.
15 – 4 = 11
If the unknown number is the minuend, simply add the two known numbers.
5 + 8 = 13
Therefore, the unknown number is 13.
13 – 5 = 8
Determining the Unknown Whole Number in an Addition or Subtraction Equation
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