Number & Algebra
Chapter 4 | Adding and subtracting decimals
Teacher Resource Sheets
Estimating answers to decimal addition & subtraction (p.88)
Is it OK to estimate? (Teacher Resource Sheet 20)
(This could be used in conjunction with "Estimating answers to decimal addition and subtraction" on page 88 of the
Student Resource Book.)
This displays some discussion points about when estimating is needed.
Example Will you have enough money at the check out?
Some examples are given that ask students to say whether it would be better to overestimate or underestimate.
Rounding practice with decimals (Teacher Resource Sheet 21)
(This could be used to revise rounding to the nearest whole number just before starting the section "Estimating the answers to decimal addition and subtraction" page 88.)
This displays a number line.
Ask
Who has spent between $4 and $5 on something recently?
Come and put the amount on the number line.
Is it nearer to $4 or $5?
What is this number to the nearest $1?
Ask
Think of something that might weigh between 45 kg and 46 kg but doesn’t have a whole number of kg.
For example, a large dog might weigh 45.7 kg
Come and put the amount on the number line.
Is it nearer to 45 kg or 46 kg?
What is this number to the nearest kg?
What number might I have been? (Teacher Resource Sheet 22)
(This could be used to revise rounding to the nearest whole number just before starting the section “Estimating the answers to decimal addition and subtraction” page 88.)
This displays some numbers and asks students what numbers could have been rounded to them.
Example
What decimal amounts could have been rounded to $17?
$17.20 rounded to the nearest whole number, etc.
Adding decimals using place value (page 90)
Break it up (Teacher Resource Sheet 23)
(This could be used as revision of partitioning decimals before teaching, “Adding decimals using place value” on page 90.)
This asks students to use place value to partition decimal numbers.
You can use this activity with a smart board, or any interactive device such as a computer, laptop or tablet.
Solving it with fractions (Teacher Resource Sheet 24)
(This is a series of slides that could be used help students to build connections between fractions and decimals prior to teaching “Adding decimals using place value” on page 90.)
This displays some decimal addition using fractions.
Example 4.6 + 3.8 = 4 6/10 + 3 8/10 = 4 + 3 + 6/10 + 8/10 etc.
You can use this activity with a smart board, or any interactive device such as a computer, laptop or tablet.
Number line additions (Teacher Resource Sheet 25)
(This is a series of slides that could be used prior to teaching “Adding decimals using place value” on page 90 and Activity 2 on page 91.)
This displays the addition 5.7 + 6.8 and shows students step by step how to use a number line to work out the answer.
You can use this activity with a smart board, or any interactive device such as a computer, laptop or tablet.
Let’s solve this with decimats (Teacher Resource Sheet 26) & Printable Master Decimats - tenths
(This could be used to help students to relate fractions and decimals before teaching “Adding decimals using place value” on page 90.)
This displays an addition for students to work out using decimats. Students could work out the answer by cutting decimats while you colour it in on the screen for discussion.
You can use this activity with a smart board, or any interactive device such as a computer, laptop or tablet. The decimats can then be coloured in.
You could use Numicon instead to illustrate this.
Subtracting decimals using place value (page 93)
Making sense of decimal subtraction with decimats (Teacher Resource Sheet 27)
(This could be used to help students understand why some decimals need to be renamed before the subtraction can take place. Use in conjunction with “Subtracting decimals using place value” on page 93.)
This displays two subtractions solved using decimats - one with renaming and one without.
Example
4.5 – 3.2 5 tenths – 2 tenth = 3 tenths
4 ones – 3 ones = 1
4.5 – 2.7 7 tenths is larger than 5 tenths
4.5 is rewritten as 3 and 15 tenths
Discuss why it is different for each subtraction.
Renaming for subtraction (Teacher Resource Sheet 28) & Printable Master Decimats - tenths
(This could be used in conjunction with “Subtracting decimals using place value” on page 93.)
Students are asked if the decimal needs to be renamed, and if it does, to rename it.
Number line subtractions (Teacher Resource Sheet 29)
(This could be used in conjunction with “Subtracting decimals using place value” on page 93.)
This displays some subtractions such as 14.3 – 8.6 and shows students step by step how to use a number line to work out the answer. You can use this activity with a smart board, or any interactive device such as a computer, laptop or tablet.
Adding and subtracting decimals using tidy numbers (p.96)
Complements (Teacher Resource Sheet 30)
(This could be used to revise complements of numbers just before "Adding and subtracting decimals using tidy numbers" page 96.)
This displays some decimals and asks students to find the complements to 1 and to 10.
How can I compensate? (Teacher Resource Sheet 31)
(This could be used to revise the two strategies that use tidy numbers just before “Adding and subtracting decimals using tidy numbers” page 96.)
This s displays some additions and subtractions and asks students to rewrite them by filling in the gaps to give some practice at rounding and compensating and using tidy numbers.
Example 15.3 – 4.9 = 15.3 – 5 + ____
Ask students to justify their choices.
Which ones? (Teacher Resource Sheet 32)
(This could be used to remind students of the sorts of numbers this strategy works well with. Use in conjunction with “Adding and subtracting decimals using tidy numbers” page 96.)
This displays some decimal addition and subtraction equations and asks students which ones it would be good to use this strategy with, in order to work out the answer.
Adding and subtracting using nested place value (page 97)
Nesting Elephants (Teacher Resource Sheet 33)
(This could be used to revise nested place value before teaching how to use this strategy to add and subtract decimals using nested place value on page 97.)
This displays some decimals and asks students to write them as tenths.
Example 14.7 = 147 tenths.
Adding and subtracting by choosing a strategy (page 98)
Story time (Getting started 4)
(This could be used in conjunction with “Adding and subtracting decimals by choosing a strategy” page 98.)
This displays the Getting started on page 85.
You could divide the class into groups and ask each group to come up with a story for each calculation given.
Which strategy? (Teacher Resource Sheet 34)
(This could be used in conjunction with “Adding and subtracting decimals by choosing a strategy” page 98.)
This displays some decimal additions and subtractions and asks students to discuss which strategy would be best to use for each and why.
You could divide the class into groups and ask them to report their discussion back to the rest of the class.
You could use an app such as Explain Everything and ask students to record an 'advertorial' to sell the advantages to the rest of the class of the strategy they have chosen to solve the problem.
