Number & Algebra
Chapter 2 | Estimating the answers to addition and subtraction problems
Teacher Resource Sheets
Checking answers by estimating (page 48)
Over or under? (Getting started 2)
(This sheet could be used as a starter for the chapter.)
This displays the Getting started on page 45.
You could use this as a group activity and ask students to report how they answered the question.
Bella's trip (Teacher Resource Sheet 7)
(This sheet could be used after the starter and prior to Activity 1 on page 48.)
This gives two scenarios where estimation might be used in real life. Students are asked whether it would be better to over or under estimate.
It’s about right isn’t it? (Teacher Resource Sheet 8)
(This sheet could be used after the starter and prior to Activity 1 on page 48. You could use it to assess prior knowledge.)
This displays a cartoon strip with an estimation mistake for students to work out.
Rounding practice (Teacher Resource Sheet 9)
(This sheet could be used as revision of rounding before beginning the teaching section on page 48.)
This displays some number lines.
Display the first number line and ask
"Who has a mother aged between 30 and 50?”
Come and put her age on the scale.
Is her age nearer to 30 or 50?
How old is she to the nearest 10?
Display the second number line and ask
Who has a phone number where the last three digits are between 100 and 200?”
Come and put the number on the number line.
Is it closer to 100 or 200?
What is the number made by the last three digits to the nearest 100?
Display the third number line and ask
Who can tell me a date between the years 1000 and 2000?”
Example: Kate Shepherd was born in 1847.
Come and put the number on the number line.
Is it nearer to 1000 or 2000?
What is this number to the nearest 1000?
You can use this activity with a smart board, or any device that allows you to interact with the image displayed on a digital device such as a computer, laptop or tablet.
What number might I have been? (Teacher Resource Sheet 10)
(This sheet could be used as a warm up or as discussion prior to the game on page 50.)
This displays some numbers and asks students what numbers could have been rounded to them.
Example
I am $200 when I am rounded.
What number might I have been?
Which estimate is best? (Teacher Resource Sheet 11)
(This sheet could be used in conjunction with Activity 1 question 3 on page 49.)
This displays some estimates for calculations and asks students which estimate is best and why.
You could ask students to work out how the other estimates were made.
Example:
67 + 69 A 156 B 120 C 140
Students might make a decision based on these reasons:
a) 140 … Accept - because rounding up would be 70 + 70.
b) 156 … Reject – this is the actual answer so no estimating is involved.
c) 120 … Reject because 60 is too far from either number.
Students could be asked to suggest a context that would prove the 120 would be an unacceptable estimate. For example, hiring a bus for groups of 67 and 69 students. 120 would be too few seats, whereas 140 would have a few spare, which is fine.
