Do you have questions about how to do lattice method multiplication? Multiplication is a skill you’ve been working on since primary school and is probably one of the most important skills you will need on your non-calculator paper. This revision sheet focuses just on the multiplication of positive numbers, including decimals. It does include some addition and subtraction too as many questions require all three of these skills.

In this series of blogs, we are going to look at three different methods for multiplication – it’s usually best to stick to the method you know but, if you are struggling, try one of the other methods.

This method, sometimes called Napier’s bones or Chinese multiplication, uses a complex grid to manage the place value. The most time-consuming part of this method is drawing the grid itself.

We place the digits for the first number across the top and the digits of the second number on the right-hand side of the grid. Then we multiply each row by each column, placing the tens digit of each answer in the left triangle and the ones digit in the right triangle.

Next, we add the digits in each diagonal part of the table, starting from the bottom right. If there is a two-digit number, we carry over the tens digit over to the next diagonal.

To identify where the decimal point is, we can either estimate the solution or map the decimal points from the original values. Trace each decimal point along a straight line until they meet. Then trace the decimals down the diagonal. As shown on the diagram.

7.84 × 9.78 = 76.6752

Example 2 Tony is buying a new motorbike. He pays a deposit of £1256 and then pays the remainder of the cost in 18 payments of £237 each. Find the total cost of the motorbike.

First, we will find the total amount paid in the 18 payments. To do this, we will calculate 237 × 18.

So, the 18 payments of £237 total £4266. We need to add this to £1256 to find the total amount spent:

So, the total amount Tony spent on the motorbike is £5522.