Auntie's age

Auntie's age

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Further Resources
This task is about using algebraic expressions to find out people's ages.
Ana is 13 and Lachlan is 11 years old. They were trying to guess their aunt's age.
Aunt Kirsty
Their aunt said,
speech bubble saying: If you double your age, Ana, and add Lachlan’s age; I’m still older than that.
 
a)
Their aunt must be more than how many years old? __________
 
 

 

Their aunt then said,

speech bubble saying: If you double your age, Ana, and add Lachlan’s age; I’m still older than that.

 
b)
Their aunt must be less than how many years old? __________
 
c)
Which expression will give you Lachlan's age if Ana's age is x?
 
  (A) x + 2
  (B) x – 2
  (C) 2x
  (D) x/2
 
Finally their aunt said,
speech bubble saying: If you double your age, Ana, and add Lachlan’s age; I’m still older than that.
 
d)
i)
 
ii)
In how many years will this be? __________
 
What must their aunt's age be now? __________
Task administration: 
This task is completed with pencil and paper only.
Level:
5
Description of task: 
Students solve algebraic problems about people's ages using information given.
Learning Progression Frameworks
This resource can provide evidence of learning associated with within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
   Y10 (09/1998)
a)   37 very easy
b)   46 very easy
c)   B easy
d) i)
ii)
20
44
[x + (x - 2) = 64, leading to x = 33. Ana will be 33, Lachlan will be 31, so this must be in 20 years' time.]
moderate
moderate