Subtract 1-Digit from 2-Digit using Models (Regrouping)
π¨ 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!
Do this: Read the concept below, then try the quiz or activity.
Concept
Sometimes, the Ones-Cubes aren't enough. We have to steal from the Tens.
π― 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: ___