7. Decimal operations

Lesson

We have learned and used tools to help us subtract whole numbers . Now we will utilise these same tools when we subtract decimals. Let's review.

Find the value of 6353 - 129.

Worked Solution

Idea summary

We can use a vertical algorithm to subtract whole numbers. We can use regrouping when necessary.

There are a few strategies that can be used to subtract a whole number from a number with a decimal. This video looks at renaming numbers.

Find 53.29-42.29, giving your answer as a decimal.

Worked Solution

Idea summary

When using the vertical algorithm to subtract decimals, it works in the same way as with whole numbers but we must remember to copy the decimal point to the same position.

Sometimes there is a need to regroup, or rename, some values before we can subtract. We use the same process as we use with whole numbers, so using place value columns can really help.

Find 3.12-0.04, leaving your answer in decimal form.

Worked Solution

Idea summary

All of the things we've been learning with decimals follow the same processes as we use with whole numbers. The only difference is the value of the digits. Saying decimals out loud can help to work out what the value of our decimals is.

This video explores how to complete a pattern that involves decimals.

Consider the following pattern.

0.63,\,0.56,\,0.49,\, ⬚,\, ⬚,\, ⬚

a

What is the pattern?

A

The numbers are decreasing by 0.7.

B

The numbers are decreasing by 7.

C

The numbers are decreasing by 0.07.

D

The numbers are decreasing by 70.

Worked Solution

b

Complete the pattern: 0.63,\,0.56,\,0.49,\, ⬚,\, ⬚,\, ⬚

Worked Solution

Idea summary

To complete a pattern of decimals, it may help to write the numbers as tenths, hundredths or thousandths or as fractions to see how the pattern changes each time.

Add and subtract decimals, with and without digital technologies, and use estimation and rounding to check the reasonableness of answers