Arithmetic Operations
Mental Multiplication Tricks
These techniques let you multiply quickly in your head — no pen, no calculator required.
1. Doubling and Halving
If one number is even, halve it and double the other. Keep doing this until one number is easy to work with.
16 × 25 → halve 16, double 25 → 8 × 50 → 4 × 100 = 400
2. Multiply by Near-10 Numbers
38 × 9 → 38 × 10 − 38 = 380 − 38 = 342
47 × 11 → 47 × 10 + 47 = 470 + 47 = 517
3. The 11-Times Trick (two-digit)
Add the digits of the two-digit number and place the sum between them.
35 × 11: 3 + 5 = 8 → answer: 3_8_5 = 385
74 × 11: 7 + 4 = 11 → carry 1 → answer: 814
4. Squaring Numbers Ending in 5
75²: multiply 7 × 8 = 56, then append 25 → 5,625
5. Breaking Into Friendly Parts
6 × 38 = 6 × 40 − 6 × 2 = 240 − 12 = 228
Summary Table
| Trick | Best for |
|---|---|
| Double/halve | One even factor |
| Near-10 | Factors near 9, 11, 19, 21… |
| ×11 trick | Any number × 11 |
| Endings in 5 | Squaring or multiplying ×5 |
Key Takeaways
- Choose the trick that suits the numbers in front of you.
- Practice each method separately before combining them.
- Estimate first: if the result is surprising, check.
Practice: Use a Mental Trick
Trick