Use Compensation to Subtract (Without a Number Line)
π€ Time to drop the number line drawing! See if you can "steal too much and give it back" entirely inside your brain.
Do this: Read the concept below, then try the quiz or activity.
Concept
Compensation is the fastest way to do massive subtraction without grabbing a pencil and paper to regroup.
π― Mental Math Steps: Problem: 53 - 18 = ? 1. See the 18. Pretend it's 20. 2. 53 - 20 = 33. 3. 20 is exactly TWO more than 18. I stole 2 extra. 4. I must GIVE 2 BACK. 5. 33 + 2 = 35. Answer: 35.
Try it
Do it in your head!
Instructions: Subtract a perfect ten, then add the extra back on!
Problem 1: 66 - 29 = ? * See 29. Make it 30. * 66 - 30 = ___ * Add 1 back: ___ + 1 = ___ * Answer: ___
Problem 2: 44 - 18 = ? * See 18. Make it 20. * 44 - 20 = ___ * Add 2 back: ___ + 2 = ___ * Answer: ___
Problem 3: 81 - 39 = ? * Answer: ___
Problem 4: 95 - 49 = ? * Answer: ___