Subtraction learning path

Subtraction Compensation: Move Both Numbers Together

The gap between two numbers stays the same if both move by the same amount. Use this to turn a tricky subtraction into one with a round number.

Free lessonLearn at your own pace

The strategy

How it works

Choose an amount that makes the number being subtracted a friendly ten.
Add that same amount to both numbers.
Subtract the adjusted numbers.

See it in action

Worked examples

Example 163 − 29

Add 1 to both numbers: 64 − 30.
64 − 30 = 34.
The difference remains 34.

Answer: 34

Example 282 − 47

Add 3 to both: 85 − 50.
85 − 50 = 35.
So 82 − 47 = 35.

Answer: 35

A quick heads-up

Common mistakes to avoid

Adjusting only one number; equal changes to both keep the gap unchanged.
Adding to the subtrahend but subtracting that adjustment from the answer, as if it were addition compensation.

Your turn

Check your understanding

Choose an answer to see instant feedback and a short explanation. You can take the quiz again any time.

Question 1 of 3

If you change 72 − 38 into 74 − 40, what did you add to each number?

Keep the momentum

Try a few practice problems

Choose a comfortable range and work through a short round with the free mental math trainer.

Practice subtraction