Subtract a Multiple of 10 from a 2-Digit Number
š 3, 2, 1, Blast off backwards! Subtracting 10, 20, or 30 is incredibly fast because the ones place completely freezes.
Concept
Just like adding groups of 10... subtracting groups of 10 is the ultimate mental shortcut. šÆ **The "Tens Only" Trick:** **Example: 57 - 30 = ?** Look at the ones place. 57 has a 7. 30 has a 0. What is 7 - 0? It's 7! The ones place is completely safe! 1. **Cover up the ones place!** Just look at the tens. 5 - 3 = 2. 2. **Put the 2 in the tens place:** The answer will start with a 2. 3. **Bring back the frozen ones place:** Bring back the 7! So, **57 - 30 = 27**! It took you 2 seconds to solve a gigantic problem!
Try it
Subtract the tens! **Instructions:** Subtract the multiples of 10 by changing ONLY the tens digit! **Problem 1: 85 - 20 = ?** * Just subtract the tens! (8 - 2 = ___) * Keep the ones frozen! * Answer: ___ **Problem 2: 43 - 10 = ?** * Answer: ___ **Problem 3: 91 - 40 = ?** * Answer: ___ **Problem 4: 68 - 60 = ?** * (Hint: 6 - 6 = 0 Tens. So the 8 flies solo!) * Answer: ___ **Problem 5: 39 - 20 = ?** * Answer: ___