With or without GST

With or without GST

Auto-markingPencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about percentages and discounts of amounts of money.

Question 1Change answer

Jen saw a jacket that she wanted to buy.
GST-jacket.png
The price tag looked like this
80-dollars-plus-gst.png
a)  If the rate of GST is 15%, what was the total cost of the jacket? $


b)  If another jacket cost $140 + GST (15%), what was its total cost? $

Question 1Change answer

GST-skirt.png
c)  If the price of a matching skirt was $200 + GST (15%), what was its total cost? $

 

d)  Another skirt cost $184 including GST (15%).
 
     What was the price of the skirt before GST was added? $
Task administration: 
This task can be completed with pencil and paper or online (with auto marking displayed to students).
Level:
5
Curriculum info: 
Maths, Number and Algebra, Number Strategies
Keywords: 
percentages, money, discount
Description of task: 
Students work out the cost of items of clothing both before and after GST has been added to them.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Multiplicative thinking, sets 8-9
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
 

Y9 (05/1997)

Y10 (05/1997)
a) $92.00 [80 × 1.15] very difficult moderate
b) $161.00 [140 × 1.15] very difficult difficult
c) $230.00 [200 × 1.15] very difficult moderate
d) $160.00 [184 ÷ 1.15] very difficult very difficult

 

Diagnostic and formative information: 
   Common error Likely calculation Likely reason
a)
b)
c)		 86. 40 or 6.40
151.20 or 11.20
216.00 or 16.00		 80 × 1.08
140 × 1.08
200 × 1.08		 8% added to the price.
a)
b)
c)		 73.60
128.20
184.00		 80 × .92
140 × .92
200 × .92		 8% deduced from the price.
a)
b)
c)
d)		 92.50
152.50
212.50
167.50		 80 + 12.50
140 + 12.50
200 + 12.50
180 – 12.50		 $12.50 used instead of 12.5%.
d) 157.50 180 – 1/8 180
180 × .875		 1/8 (i.e., 12.5%) deduced instead of 1/9.