There's a handy thing you can do with a $10$10 x $10$10 grid, and it allows you to work out the answer to a multiplication, such as this one: $0.1$0.1 × $0.1$0.1. In fact it works for any multiplication of two decimals with tenths!

How does it work?

I'm glad you asked, because it means you can use rules such as this, trusting that they work. Let's take a look at why it works, in this video, and work through a couple of examples.

Anyone for colouring?

If you have some 10 x 10 grids (you can even make your own), you might like to create some problems, and then solve them by colouring the two decimals. Find the overlap, and that's your answer to the multiplication of your two decimals.

Worked Examples

Question 1

Use the grid to find the value of $0.1\times0.7$0.1×0.7.

Write the answer as a decimal.

Question 2

Use the grid to find the value of $0.5\times0.1$0.5×0.1.

Write the answer as a decimal.

Question 3

Use the grid to find the value of $0.7\times0.8$0.7×0.8.

Write the answer as a decimal.

Outcomes

NA5-3

Understand operations on fractions, decimals, percentages, and integers