Learn the idea
Break each number into tens and ones. Each part of one factor must multiply every part of the other factor. Adding all partial products gives the full product.
- Write each factor as tens plus ones.
- Multiply every pair of parts.
- Add all partial products.
LET’S WORK IT OUT
Worked example
Calculate 23 × 14.
200 + 80 + 30 + 12 = 322
(20 + 3) × (10 + 4) gives 20 × 10, 20 × 4, 3 × 10, and 3 × 4.
A mistake to watch for
Multiplying only tens by tens and ones by ones leaves out two partial products.
Helpful skills to know first
YOUR TURN
Try three practice questions
Enter your answer, then check the explanation. You can also open each explanation to study it. These three questions check understanding; they are not a mastery score.
Question 1
Calculate 12 × 13.
Answer and explanation
156 — 120 + 36 = 156, or 100 + 30 + 20 + 6.
Question 2
Calculate 24 × 15.
Answer and explanation
360 — 24 × 10 = 240 and 24 × 5 = 120; add them.
Question 3
Calculate 32 × 21.
Answer and explanation
672 — 32 × 20 = 640 and 32 × 1 = 32; add them.
For parents and teachers
Draw a rectangle split into four regions and label each partial product.
Ask your learner to explain the method before moving on. This lesson covers one focused skill and is not a complete curriculum assessment.