Washing machine repairs II

Washing machine repairs II

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about calculations with linear equations.

Tawera's Community Electrical use this equation to work out how much they will charge to fix a washing machine.
 
 
c = 30 + 28h      c = the cost of repairs (in dollars)
                          h = the time the repairs take (in hours).
 
a)
Alipate's machine took 3 hours to fix. How much did this cost? $___________
 
b)
Wanda's machine cost $170 to repair. How many hours did this take?
Show all your working and then write your answer in the box.
 
 
 
 
 
 
 
 
 
 
 
 

 
Wanda's machine took __________ hours to fix. 
Task administration: 
This task is completed with pencil and paper only.
Level:
5
Curriculum info: 
Maths, Number and Algebra, Equations and expressions
Key Competencies: 
Using language, symbols, and texts
Keywords: 
linear equations, substitution
Description of task: 
Students use substitution to calculate the cost and length of time taken to repair washing machines, and formulate and solve a related linear equation.
Curriculum Links: 
Key competencies
This resource involves formulating and showing how to solve a simple linear equation. This relates to the Key Competency: Using language, symbols and text.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Using symbols and expressions to think mathematically, sets 6-7
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 

 

  

Y10 (11/1999)

1 mark

a)

114

moderate

2 marks
(Correct answer and working)
or
1 mark
(Correct answer or 1 error in working with an answer consistent with the working)

b)

Examples of correct working include:

•    30 + 28h = 170
•    28h = 170 - 30
•    28h = 140
•     h = (c - 30) div 28
•     h = (170 - 30) ÷ 28
•     170 - 30 = 140
•     140 ÷ 28 = 5
•     Answer: 5

2 correct – difficult

1 correct – moderate

NOTE: In b) count mathematically incorrect equations such as 170 - 30 = 1408 ÷ 28 = 5 as being equivalent to an error and score as 1 mark.

Diagnostic and formative information: 

  

Common error

Likely calculation

Likely reason

a)

33
84

30 + 3
28 × 3

Adds dollars to hours.
Forgets to add 30.

b)

140

170 - 30

Forgets to divide by 28.