Stage 15 of 20
Multiplying by 9 and 11
Special patterns for 9 and 11 make these “scary” tables feel playful — and highly memorable for learners.
Pattern power
For ×11 with single digits: duplicate the digit (4 × 11 = 44). For ×9: use ×10 minus the number, or the finger trick / digit-sum-to-9 pattern for 1–9.
Why this mental math skill matters
Pattern-based facts for 9 and 11 are memorable and motivating. Patterns still rest on real properties — ×9 as ×10−1, ×11 digit duplication for 1–9.
Worked examples
Study each example slowly. Say the steps aloud — verbal rehearsal strengthens mental arithmetic memory.
6 × 11
- Duplicate the digit 6.
- 66.
Answer: 66
7 × 9
- 7 × 10 = 70.
- Subtract 7.
- 63.
Answer: 63
8 × 9
- Digits of the product add to 9: 7 + 2 = 9.
- Or 80 − 8 = 72.
Answer: 72
Tips for success
- For single-digit ×11, duplicate the digit.
- For ×9, use ×10 minus the number.
- Check ×9 products: digits often sum to 9 for 1–9.
Common mistakes to avoid
- Applying the ×11 digit trick to two-digit factors incorrectly.
- Using the digit-sum pattern without verifying occasionally.
How to practice this stage
Alternate pattern practice with “explain why it works” prompts so the shortcut stays meaningful.
Interactive practice
Stage 15 Drill
Apply the ×9 or ×11 pattern.
Solve
—
FAQ: Multiplying by 9 and 11
What is the mental math trick for multiplying by 11?
For a single digit n, n × 11 is written as nn (for example, 4 × 11 = 44).
How do you multiply by 9 in your head?
Multiply by 10, then subtract the original number: 7 × 9 = 70 − 7 = 63.