Use compensation to add: up to three digits
⚖️ Want to do mental math like a wizard? Use "compensation" to turn ugly numbers into friendly ones before you add!
Do this: Read the concept below, then try the quiz or activity.
Concept
Sometimes adding big numbers looks scary, like 398 + 245. But 398 is extremely close to a "friendly" number (400!). We can use compensation to make it easier.
🎯 How Compensation Works: Think of addition like a balance scale. If you add weight to one side, you must take it away from the other side. Example: 398 + 245 = ? 1. Make a Friendly Number: 398 needs just 2 more to become 400. 2. Borrow from the Other Number: If I add +2 to 398, I must subtract -2 from 245. 3. The New Problem: (398 + 2) = 400 (245 - 2) = 243 4. Add the Friendly Numbers: 400 + 243 = 643! So, 398 + 245 = 643.
Try it
Turn these ugly problems into friendly ones!
Instructions: Adjust the numbers to make the addition easier, then solve.
Problem 1: 199 + 350 * 199 needs 1 to become 200. * Subtract 1 from 350 (it becomes ___). * Add: 200 + ___ = ___
Problem 2: 495 + 120 * 495 needs 5 to become 500. * 120 minus 5 is ___. * Add: 500 + ___ = ___
Problem 3: 298 + 104 * Evaluate and Answer: ___
Problem 4: 990 + 35 * Evaluate and Answer: ___