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Determining the Unknown Whole Number in an Addition or Subtraction Equation 1st Grade Math Worksheets

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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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