Lesson 13 of 16Article15 min
Integers Deep Dive & Mental Math
Fluent integer arithmetic frees working memory for harder problems. Use compensation, breaking apart, and compatible numbers instead of counting on fingers.
Speed with structure
Fluent integer arithmetic frees working memory for harder problems. Use compensation, breaking apart, and compatible numbers instead of counting on fingers.
- Compensation: 398 + 47 = 400 + 47 − 2 = 445.
- Break apart: 24 × 5 = (20 × 5) + (4 × 5) = 120.
- Compatible: 25 × 16 = 25 × 4 × 4 = 100 × 4 = 400.
- Estimate first: does 19 × 21 ≈ 400 feel right? (Yes — (20−1)(20+1)=400−1.)