Exercise 2: Working with 5
Now it's time to master the thumb (value 5)! Every problem in this exercise includes the number 5 either in the calculation or result. All intermediate and final results stay within 1–5, using your right hand only.
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Show the result on your right hand
Conversion Technique: Thumb and Other Fingers
Basic Rules:
- Extended finger = counting
- Bent finger = not counting
- 4 fingers (index, middle, ring, pinky) = 1 each
- Thumb = 5
Key Principles:
- When thumb is extended and want to subtract one → thumb bends, 4 other fingers extend
- When 4 fingers are extended and want to add one → thumb extends, 4 other fingers bend
Example: 2 + 3 = 5
Step 1: Extend 2 fingers (index + middle) = 2
Step 2: Add 3 means need to extend 3 more fingers
- Extend ring finger = 3
- Extend pinky = 4
- Out of fingers! Need 1 more finger
Step 3: Conversion
- Bend all 4 fingers
- Extend thumb → 5!
Explanation: 2 + 3 = 5 is actually 2 + 2 = 4, then 4 + 1 = 5 (convert 4 fingers to thumb)
Example: 5 - 2 = 3
Step 1: Extend thumb = 5
Step 2: Subtract 2 means need to reduce by 2 units
- Need to subtract 1 first: Bend thumb
- But no other fingers extended to bend!
Step 3: Conversion
- Bend thumb
- Extend all 4 fingers = 4
- Continue subtracting:
4 - 1 = 3→ Bend pinky
Result: 3 fingers extended (index + middle + ring) = 3
Explanation: 5 - 2 = 3 is actually 5 - 1 = 4 (convert thumb to 4 fingers), then 4 - 1 = 3
Quick Conversion Reference:
| Calculation | Action |
|---|---|
4 + 1 = 5 | Bend 4 fingers → extend thumb |
5 - 1 = 4 | Bend thumb → extend 4 fingers |
3 + 2 = 5 | Extend 1 more (= 4), then convert to 5 |
2 + 3 = 5 | Extend 2 more (= 4), then convert to 5 |
5 - 2 = 3 | Convert to 4, then bend 1 finger |
💡 Tip: Practice the conversion slowly at first. The key is understanding that 4 fingers + 1 = thumb (5) and thumb - 1 = 4 fingers. Speed comes with repetition!
Learning Goals
- Master using the thumb for 5
- Understand conversion between 4 fingers ↔ thumb
- Smooth transitions in multi-step problems
- Build foundation for numbers 6-9
Key Concept
Right Hand Values:
- Thumb = 5
- Index finger = 1
- Middle finger = 1
- Ring finger = 1
- Pinky = 1
Remember: When thumb is extended, the 4 fingers are bent. When 4 fingers are extended, thumb is bent.