What you need to know
Multiplication is a fast way of adding equal groups. 4 × 6 means 4 groups of 6, which is 6 + 6 + 6 + 6 = 24. Instead of adding over and over, we learn strategies that get us to the answer quickly and let us check that it is right.
Arrays. An array is a set of objects arranged in equal rows and columns, like eggs in a carton. 3 rows of 5 dots shows 3 × 5 = 15. Turn the array on its side and you see 5 rows of 3, which is 5 × 3 = 15. The answer does not change when you swap the numbers. These are called turn-around facts, and they halve the number of facts you need to learn.
Use an array for 4 × 6
- Draw 4 rows with 6 dots in each row.
- Count the rows in sixes: 6, 12, 18, 24.
- So 4 × 6 = 24.
- Turn it around: 6 rows of 4 is 6 × 4, and counting in fours gives 4, 8, 12, 16, 20, 24. Same answer.
Splitting an array (partial products). If a fact is hard to remember, split one of the numbers into friendlier parts, multiply each part, then add the answers together. The two smaller answers are called partial products. The 5s and 10s are the easiest facts to split around.
7 × 8 by splitting the 7
- Split 7 into 5 and 2 (because the 5 times table is easy).
- 5 × 8 = 40.
- 2 × 8 = 16.
- Add the partial products: 40 + 16 = 56. So 7 × 8 = 56.
Bigger numbers. The same idea works for a two-digit number times a one-digit number. Split the two-digit number into its tens and ones, multiply each part, then add.
23 × 3 using partial products
- Split 23 into 20 and 3.
- Multiply the tens: 20 × 3 = 60.
- Multiply the ones: 3 × 3 = 9.
- Add: 60 + 9 = 69. So 23 × 3 = 69.
| Fact | Split | Partial products | Answer |
|---|
| 6 × 7 | (5 × 7) + (1 × 7) | 35 + 7 | 42 |
| 8 × 9 | (8 × 10) − (8 × 1) | 80 − 8 | 72 |
| 14 × 5 | (10 × 5) + (4 × 5) | 50 + 20 | 70 |
| 32 × 4 | (30 × 4) + (2 × 4) | 120 + 8 | 128 |
Common mistake: when splitting 23 × 3, working out 2 × 3 = 6 instead of 20 × 3 = 60. The 2 in 23 is worth 20, so the answer is 69, not 15. Say the value of the digit out loud before you multiply.
Check yourself
- An array has 3 rows with 7 dots in each row. What multiplication fact does it show, and what is the answer?
- What is the turn-around fact for 5 × 4, and what is the answer?
- Split 6 × 8 into (5 × 8) + (1 × 8). What is the answer?
- 12 × 3 = ?
- 24 × 4 = ?
- Work out 9 × 7 using (10 × 7) − (1 × 7).
Answers: 1. 3 × 7 = 21 2. 4 × 5 = 20 3. 40 + 8 = 48 4. 36 (30 + 6) 5. 96 (80 + 16) 6. 70 − 7 = 63