7. Decimal operations

Lesson

Let's review a strategy for multiplying whole numbers .

Calculate 26\times39 by completing an area model.

a

Firstly, complete the missing values in the area model.

\times | 20 | 6 |
---|---|---|

30 | ||

9 |

Worked Solution

b

Now add the values you found in part a to calculate 26\times39.

Worked Solution

Idea summary

We can use area models to multiply two digit numbers.

This video looks at how to use the area model to multiply numbers with decimals.

Use the area model to find 47 \times 5.4.

a

Fill in the areas of each rectangle.

Worked Solution

b

What is the total area of the four rectangles, and the answer to 47\times5.4?

Worked Solution

Idea summary

We can use area models to multiply decimals.

This video shows how to multiply a decimal number in the hundredths by a 2 digit number, using the same processes as for whole numbers, while thinking about the placement of the decimal point.

We want to find 43\times 1.06.

a

First, choose the most reasonable estimate for 43\times1.06.

A

91

B

23

C

43

Worked Solution

b

Find 43\times 1.06, giving your answer as a decimal.

Worked Solution

Idea summary

When we work with decimals, we can use all of the strategies we used with whole numbers, including the area model and vertical algorithm. The important difference is the value of the digits. Digits to the right of the decimal point are fractions, so they are worth less.