Overview
This lesson shows fun and easy tricks to help you multiply numbers in your head super fast.
Multiplying Two-Digit Numbers by 11
- To multiply a two-digit number by 11, add the two digits and put the answer in the middle.
- Example: 43 × 11 → 4, (4+3=7), 3 → answer is 473.
- If the middle number is 10 or more, add the extra to the first digit.
- Example: 68 × 11 → 6, (6+8=14, so add 1 to 6), 8 → answer is 748.
Multiplying Three-Digit Numbers by 11
- Write the first and last numbers. In the middle, add each pair of neighbors.
- Example: 352 × 11 → 3, (3+5=8), (5+2=7), 2 → answer is 3872.
- If you get 10 or more, add the extra to the number before it.
- Example: 574 × 11 → 5, (5+7=12, add 1 to 5), (7+4=11, add 1 to 7), 4 → answer is 6314.
Multiplying Numbers Ending in 5 (Same First Number)
- For numbers like 75 × 75: multiply the first number by the next number, then write 25.
- Example: 75 × 75 → 7×8=56, then 25 → answer is 5625.
- Example: 35 × 35 → 3×4=12, then 25 → answer is 1225.
Multiplying Numbers (Same First Number, Last Numbers Add to 10)
- For numbers like 44 × 46: multiply the first number by the next number, then multiply the last numbers.
- Example: 44 × 46 → 4×5=20, 4×6=24 → answer is 2024.
- Example: 67 × 63 → 6×7=42, 7×3=21 → answer is 4221.
Tips
- If you get a big number in the middle, add the extra to the number before it.
- Practice these tricks to get even faster!