Missing Subtrahend

Missing Subtrahend

When you know the starting number and the result after subtraction, you can find the missing number that was taken away.

Key idea

Use the relationship:

start − missing number = difference

To find the missing subtrahend, ask: What must be subtracted from the starting number to get the difference?

Steps

1. Identify the starting number.
2. Identify the difference or result after subtraction.
3. Think of the subtraction sentence as a missing part problem.
4. Find the number that makes the equation true.

You can do this by checking nearby numbers, or by using the inverse idea: subtraction undoes addition. So if you know the start and the difference, the missing number is the amount needed to go from the difference back up to the start.

Check your answer

Substitute your answer back into the subtraction sentence. If the calculation gives the known difference, your answer is correct.

Example method

If the sentence is “12 − __ = 5,” ask: “12 minus what equals 5?” The missing number is the amount that bridges 5 up to 12.

Always verify by subtracting your answer from the starting number.