Disappearing dollars
This is a level 4 number activity from the Figure It Out series. It is focused on adding and subtracting integers using money context. A PDF of the student activity is included.
About this resource
Figure It Out is a series of 80 books published between 1999 and 2009 to support teaching and learning in New Zealand classrooms.
This resource provides the teachers' notes and answers for one activity from the Figure It Out series. A printable PDF of the student activity can be downloaded from the materials that come with this resource.
Specific learning outcomes:
- Add and subtract integers using money context.
Disappearing dollars
Achievement objectives
NA4-2: Understand addition and subtraction of fractions, decimals, and integers.
Required materials
- Figure It Out, Level 3–4, Number, Book 1, "Disappearing dollars", page 24
- toy money
See Materials that come with this resource to download:
- Disappearing dollars activity (.pdf)
Activity
This activity uses addition, subtraction, and the concept of integers in a real-life context.
The students need to understand the concept of what happens when you subtract a bigger number from a smaller number:
- What happens when you get less than zero?
- Can you get less than zero?
and so on.
Money is a nice way to introduce the idea of negative numbers because most students have some concept of being in debt or owing someone money. You could combine this with a number line.
For example:
- You have $5. You owe your mother $10 and want to pay her back. You give her the $5. How much money do you have now? (You actually have $0, but you still owe your mother $5, so you are $5 in debt.)
- Show this on a number line.
Questions 3c and d introduce the idea of negatives in a nice gentle way. The answers say Georgia needs $5 more to pay her bills rather than saying Georgia has minus $5 or is $5 in debt. You could ask the students to demonstrate Georgia’s situation on a number line, which would introduce the idea of negative numbers if you don’t use the scenario above.
1.
$3
2.
a. None
b. He would have $20 left.
3.
a. Yes. Frank has $18 worth of bills and $19 cash.
b. Yes. Sally has $21 worth of bills and $25 cash.
c. No. Georgia needs $5 more to pay her bill.
d. No. Charlotte needs $9 more to pay her bills.
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