Subtract 1-Digit from 2-Digit using Models (Regrouping)
šØ Break apart the rod! What happens when you need to subtract 5 ones, but you only have 2? You have to smash a Tens-Rod to get more pieces!
Concept
Sometimes, the Ones-Cubes aren't enough. We have to steal from the Tens. šÆ **The "Smash a Ten" Trick:** **Example: 32 - 5 = ?** 1. **Draw it:** 3 long Tens-Rods, and 2 little Ones-Cubes. 2. **The Problem:** We need to cross out 5 little cubes. But we only have 2! Oh no! 3. **Smash a Ten:** Take one of the 3 long Rods, and SMASH it into 10 little cubes! 4. **The New Picture:** Now we only have 2 safe Tens-rods. But we have a pile of 12 little Ones-cubes! (The 10 we smashed + the 2 old ones). 5. **Cross them out:** Take away 5 of the 12 cubes. (12 - 5 = 7). 6. **Count the answer:** You have 2 rods and 7 cubes. 7. **Answer:** **27**!
Try it
Smash the rod to get more pieces! **Instructions:** Imagine smashing one 10-rod into 10 pieces so you can subtract! **Problem 1: 41 - 4 = ?** * Model: 4 Rods, 1 Cube. * Cross out 4? I can't! Smash a rod! * New Model: 3 Rods, 11 Cubes. * Now do 11 - 4 = ___ * Answer: 3 Rods and ___ Cubes = ___ **Problem 2: 25 - 8 = ?** * Smash a rod! (Leaves 1 rod. Makes 10 extra cubes). * 15 Cubes - 8 = ___ cubes. * Answer: ___ **Problem 3: 53 - 5 = ?** * Answer: ___ **Problem 4: 16 - 9 = ?** * Answer: ___