Comparing prices

Comparing prices

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Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about adding together costs and working out the cheapest option.

Matu with a paddle

Matu's waka ama team wanted to get prices for some gear.

Question 1Change answer

They need to buy a paddle, 2 dry bags, and 2 rolls of grip tape.
Matu gets the price from 3 stores.
 
Write the total cost for each of the 3 stores. 
  Store 1 Store 2 Store 3
Paddle $370 $400 $410
Dry bags (×2) $33 × 2 $20 × 2 $16 × 2
Grip tapes (×2) $12 × 2 $8 × 2 $10 × 2
TOTAL COST a)   $  b)   $  c)   $ 
d) Which store should they buy from and why?
Task administration: 
This task can be completed with pen and paper or online (with SOME auto marking).
Level:
4
Curriculum info: 
Maths, Number and Algebra, Number Strategies
Keywords: 
multiplication, addition, money
Description of task: 
Students use addition and multiplication to work out the cheapest of several price options.
Curriculum Links: 

This resource can be used to help to identify students' understanding of adding and multiplying whole numbers (Number Strategies).

Learning Progression Frameworks
This resource can provide evidence of learning associated with
Additive thinking, sets 7-8
Multiplicative thinking, sets 6-7
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
  Correct answer Y8 (11/2013)
a) 460 very easy
b) 456 very easy
c) 462 very easy
d)
Store 2 [or answer consistent with a)-c)]
Explanation about which store is cheapest overall
Examples:
  •   Store 2 because it is the cheapest.
  •   Store 2 is a better deal than the other stores.
  •   He should buy from store one due to the lower price.
  •   It is $4 cheaper [than the next cheapest  store]
Accept: if student also points out that buying the items individual from the cheapest store as long as they identify Store 2 is cheapest overall.
very easy
very easy

Based on an online sample of 62 Year 8 students

Diagnostic and formative information: 
  Answer given Likely misconception Next Steps
a) 450 Students do not "carry" the ones  when adding 66 + 24 Students could explore strategies such place value partitioning [e.g., 66 + 24 = (60 + 20) + (6 + 4) = 80 + 10 = 90]
d) Different shops Students do not recognise that the the items are to be bought at just one shop.