Savings account II

Savings account II

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This task is about using an equation to calculate the amount of money in a bank account.
girl standing outside a bank
Hayley's Papa said "Here is $20 to open a savings account. For every one dollar you put into your account I will give you another 50 cents to put in." 
 
The total amount in Hayley's account can be written as the equation:

T = 20 + 1.5m

where 
  T = total amount in Hayley's savings account ($)
  m = amount Hayley puts in ($)

Question 1Change answer

a) Use the equation to help you complete the total amount in her account for each amount she has put in.

Amount Hayley puts in, m ($) 0 10 20 30 40
Total amount in account, T ($)

Question 2Change answer

b) If Hayley puts in $200 what would be the total amount in her account?  $ 
c) If the total amount in her account was $620, how much had Hayley put in the account? $ 
d) If the total amount in the account was $170, altogether how much had Hayley's Papa
     put in the account? $ 
Task administration: 
This task can completed with pencil and paper or online (with auto-marking).
Level:
5
Curriculum info: 
Maths, Number and Algebra, Equations and expressions
Keywords: 
linear equations, rules, substitution, money, saving, banking
Description of task: 
Students demonstrate their understanding of a linear algebraic equation to calculate the amount of money in a savings account.
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 (08/2001)

a)

20, 35, 50, 65, 80

moderate

b)

320

moderate

c)

400

moderate

d)

70

very difficult
Diagnostic and formative information: 
 

Common error

Likely miscalculation

Likely reason

a)

0, 15, 30, 45, 60

T = 1.5 m

Excludes the $20 from the calculation.

b)

300

T = 1.5 × 200

c)

310
465

T = 620 / 2
T = 1.5 × 620
         2

  

d)

50
 
85

  
 
170 / 2

Does not include the initial $20 put into account by the grandfather.