Subtract by Counting Back - Up to 20
š§ Put away the number line, it's time to count back in your head! You can subtract small numbers quickly just by counting backward.
Concept
Once you are good at hopping on a number line, you can do those hops right inside your brain! This is called "counting back". šÆ **The "Count Back" Strategy:** This works best when you are only subtracting a small number, like 1, 2, 3, or 4. **Example: 17 - 3 = ?** 1. **Start with the big number:** Say "17" out loud and put it in your head. 2. **Hold up fingers for the small number:** Hold up 3 fingers. 3. **Count backward and put down a finger each time:** Say "16" (put down 1), "15" (put down 1), "14" (put down the last finger). 4. **The last number you said is the answer!** So, **17 - 3 = 14**. If the number you are subtracting is really big (like 17 - 15), this strategy takes too long. But for small take-aways, it's perfect!
Try it
Time to count backward in your head! **Instructions:** Start at the big number and count backward to find the answer. **Problem 1: 16 - 2 = ?** * Start at 16. Count back 2: "___, ___" * Answer: ___ **Problem 2: 19 - 4 = ?** * Start at 19. Count back 4. * Answer: ___ **Problem 3: 13 - 1 = ?** * Answer: ___ **Problem 4: 20 - 3 = ?** * Answer: ___