Level 3 · Basic Multiplication
2-by-1 Left-to-Right Multiplication
Multiply a two-digit number by a single digit by breaking it into two tiny multiplications — both easy enough to do mentally.
The Method
Use the distributive property: split the two-digit number into its tens and units parts, multiply each by the single digit, then add the two results.
Worked Example
42 × 7
- Split 42 → tens part 40 + units part 2
- 40 × 7 = 280
- 2 × 7 = 14
- 280 + 14 = 294
Why Left-to-Right?
Multiplying the tens part first gives you the big part of the answer immediately (280), and you only need to add a small correction (14). If you lose track, you still have a useful approximation. Right-to-left multiplication forces you to hold a growing number of "carried" values in working memory simultaneously.
Another Example
78 × 6
- Split: 70 + 8
- 70 × 6 = 420
- 8 × 6 = 48
- 420 + 48 = 468
💡 Teaching Tip
Once students are comfortable, challenge them to "say the partial product as soon as they compute it" — "280... plus 14... 294." The verbal cue of announcing the partial product builds working memory habits essential for harder tricks later.