Multiplication with arrays & the area model
Theory
An array sets objects out in equal rows and columns, so the total is rows \(\times\) columns. The area model draws a multiplication as a rectangle and splits it by place value into easier partial products. This Year 5 maths page shows arrays, turning arrays round, using arrays to divide, and using the area model to multiply two-digit numbers by one-digit numbers.
An array is an arrangement of objects in equal rows. An array with \(6\) rows of \(7\) shows \(6 \times 7 = 42\).
Turning an array on its side swaps the rows and columns but keeps the same number of objects, so \(6 \times 7 = 7 \times 6\). This is the commutative law: the order of multiplying does not matter.
Arrays also show division: \(56\) counters in \(7\) equal rows gives \(56 \div 7 = 8\) in each row.
The area model draws \(6 \times 37\) as a rectangle \(6\) high and \(37\) wide, split into \(6 \times 30\) and \(6 \times 7\). Each part is a partial product; adding them gives the answer.
Arrays and area models both use rows times columns:
How to use the area model
- Draw a rectangle with the one-digit number down the side.
- Split the two-digit number into tens and ones along the top.
- Multiply to find the area of each part.
- Add the partial products.
How to use an array to divide
- Share the total into the given number of equal rows.
- Count how many are in each row.
| \(7 \times 10\) | \(=\) | \(70\) |
| \(7 \times 3\) | \(=\) | \(21\) |
| \(70 + 21\) | \(=\) | \(91\) |
There are \(91\) chairs.
| \(3 \times 9\) | \(=\) | \(27\) |
| \(9 \times 3\) | \(=\) | \(27\) |
Still \(27\) objects, now in \(9\) rows of \(3\).
| \(56 \div 7\) | \(=\) | \(8\) |
\(8\) tiles in each row, because \(7 \times 8 = 56\).
| \(4 \times 50\) | \(=\) | \(200\) |
| \(4 \times 8\) | \(=\) | \(32\) |
| \(200 + 32\) | \(=\) | \(232\) |
\(4 \times 58 = 232\).
| \(9 \times 20\) | \(=\) | \(180\) |
| \(9 \times 3\) | \(=\) | \(27\) |
| \(180 + 27\) | \(=\) | \(207\) |
The area is \(207\) square metres.
| \(37 - 30\) | \(=\) | \(7\) |
| \(180 + 42\) | \(=\) | \(222\) |
The box is \(7\), and \(6 \times 37 = 222\).
| \(3 \times 40\) | \(=\) | \(120\) |
| \(3 \times 7\) | \(=\) | \(21\) |
| \(120 + 21\) | \(=\) | \(141\) |
The \(4\) means \(40\), so the parts are \(40\) and \(7\). The answer is \(141\).
Common pitfalls
Frequently asked questions
What is an array in maths?
An array is a set of objects in equal rows and columns. \(6\) rows of \(7\) show \(6 \times 7 = 42\).
Why does turning an array not change the total?
The same objects are just viewed the other way, so \(3 \times 9 = 9 \times 3\). This is the commutative law.
What is the area model for multiplication?
It draws the multiplication as a rectangle, splits one side by place value and adds the areas of the parts: \(4 \times 58 = 200 + 32 = 232\).
What is a partial product?
One of the smaller products in a split multiplication, such as \(4 \times 50\) and \(4 \times 8\) in \(4 \times 58\).
How can an array show division?
Share the objects into equal rows. \(56\) in \(7\) rows gives \(8\) per row, so \(56 \div 7 = 8\).