Dinosaur algebra

Dinosaur algebra

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This task is about using algebraic equations.

Question

a)  A triceratops weighed four times as much as a stegosaurus. Together they weighed 15 tonnes.
     Here is an equation describing their total weight.
x + 4x = 15
  i) What does the x in the equation stand for?

    • The weight of the triceratops.

    • The weight of the stegosaurus.

    • The number of dinosaurs.

    • The total weight of the two dinosaurs.

    • The difference in weight between the two dinosaurs.

Question

  ii)  What is the weight of the stegosaurus?

    • 1 tonne

    • 3 tonnes

    • 4 tonnes

    • 12 tonnes

    • 15 tonnes

Question

A brontosaurus weighed 3 times as much as a triceratops. Together they weighed 48 tonnes.
The equation shows their total weight.
y +   y = 48
To complete the equation correctly, what number should be in the box above?

    • 1

    • 2

    • 3

    • 4

    • 8

Task administration: 
This task can be completed with pencil and paper or online with auto-marking.
Level:
4
Curriculum info: 
Maths, Number and Algebra, Equations and expressions
Keywords: 
linear equations, rules, pronumerals
Description of task: 
Students describe a variable in a linear equation, solve the equation, and complete a second equation relating to weights.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Using symbols and expressions to think mathematically, sets 4-5
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
 

Y8 (09/2000)
a) i) The weight of the stegosaurus (B) difficult
   ii) 3 tonnes (B) moderate
b)    4 tonnes (C) moderate
Diagnostic and formative information: 
  

Common error

Likely reason

a) i)

    ii)

The weight of the triceratops (A) 
The difference in weight between the two dinosaurs (E)
4 tonnes (C)

12 tonnes (D)

x is triceratops, 4x is stegosaurus.

Assumes the "4" is the weight of the Stegosaurus and does not 
take "x" into account.
This is weight of triceratops (4x = 12).

b)

4 (D)
8 (E)

Uses format from equation in question a).