Rewriting formula

Rewriting formula

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about re-arranging equations to make x the subject.
Re-write each of the formulae below to make x the subject.
 
a)
y = x + 4
 
x = ____________________
 
b)
y = 3x
 
x = ____________________
 
c)
y = x⁄5
 
x = ____________________
 
d) 
y = 5x2
 
x = ____________________
 
e)
y = 2x - 1
 
x = ____________________
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: 
algebraic expressions, changing subject
Description of task: 
Students are required to re-arrange various algebraic equations.
Curriculum Links: 

Key competencies

This resource involves showing how to change the subject of an 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 (11/2002)
a) y - 4 easy
b) y / 3 or 1/3 y moderate
c) 5y very difficult
d) easy
e) (y + 1) / 2 or 1/2 (y + 1) difficult
Diagnostic and formative information: 
 

Student response

Likely miscalculation

Likely misconception
a)

4 - y

y = x + 4 means 0 = x + 4 - y

  
b)

3/y

y = 3x means 1 = x.3/y

  

d)

1/2 y + 1 or y + 1 ÷ 2

Correct answer if brackets put in appropriate place.

  

a)
b)
c) 
d) 
e)

y + 4
3y
y/5
5y2
2y - 1

 

Substitutes y for x in equation or uses operation rather than inverse operation (e.g., + 4 to each rather than - 4).