Use models to subtract two-digit numbers - with regrouping
Not enough ones? No problem! 🙅♀️ We can trade a ten rod for 10 ones. This is regrouping in subtraction, and it lets us solve any subtraction problem!
Concept
Regrouping in subtraction is what we do when we don't have enough 'ones' to subtract from. We need to 'borrow' from the tens place. **Visual:** Let's solve 42 - 15 using place value blocks. 1. Show 42 with 4 ten rods and 2 one cubes. 2. We need to subtract 15 (1 ten and 5 ones). Let's start with the ones. Can we take 5 ones away from 2 ones? Nope! 3. We need to **regroup**. Take 1 of the ten rods and trade it for 10 one cubes. 4. Now we have 3 ten rods and 12 one cubes (our original 2 plus the 10 we just got). It's still the number 42, just shown differently! 5. Now we can subtract the 5 ones. 12 - 5 = 7. We have 7 ones left. 6. Next, subtract the tens. We have 3 ten rods left, and we need to subtract 1 ten rod. 3 - 1 = 2. We have 2 tens left. 7. What's our final answer? 2 ten rods and 7 one cubes. That's 27! So, 42 - 15 = 27. **Key Idea:** If the top number's ones digit is smaller than the bottom number's, you must regroup. Borrow a ten from the tens place and turn it into 10 ones to give yourself enough to subtract.
Try it
Practice: Use models to subtract two-digit numbers - with regrouping.