Scroll of the Combo

Mirror Stance

13 × 7 is exactly the same as 7 × 13. If you know the tables to 10, you already know half of every bigger table.

Practice: Only the pairs where both numbers are above 10 are new, such as 12 × 14.

Split and Conquer

Break one number into tens and ones, multiply each part, then add.

Practice: Try 16 × 12, 18 × 15 and 23 × 4.

Eleven Palms

To multiply a two-digit number by 11, split the digits and put their sum in the middle.

If the sum is 10 or more, carry 1 to the first digit: 75 × 11 → 7 + 5 = 12 → 7+1, 2, 5 = 825.

Practice: Try 42 × 11, 36 × 11 and 87 × 11.

Tiger's Five

To square a number ending in 5, multiply the first digit by the next whole number, then write 25 after it.

Practice: Try 25², 45² and 65².

Double and Halve

Halve one number and double the other — the product stays the same. Perfect when one number is even and the other ends in 5.

Practice: Try 16 × 5, 18 × 15 and 24 × 25.

Anchor Squares

Learn the squares from 11 to 20 by heart. They are fixed points you can step from.

11² = 121 · 12² = 144 · 13² = 169 · 14² = 196 · 15² = 225 · 16² = 256 · 17² = 289 · 18² = 324 · 19² = 361 · 20² = 400

Practice: Use 15² = 225 to find 15 × 16 and 14 × 15.

Ten Trick

For two numbers between 11 and 19: add the ones digit of one to the other, add a zero, then add the product of the ones digits.

Practice: Try 14 × 13, 16 × 12 and 17 × 18.

Middle Path

When two numbers sit evenly around a round number, square the middle and subtract the distance squared.

Practice: Try 18 × 22 (400 − 4) and 29 × 31.