Building a fence

Building a fence

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about multiplying with decimals.
To build a fence across their section Toni needed fence posts, lengths of timber, and palings.
 

illustration: person kneeling with hammer

a) Calculate the total length of ...
 
 
i)
 
ii)
 
iii)
4 fence posts, each 2.1 m long. __________ metres
 
6 lengths of timber, each 2.4 m long. __________ metres
 
46 palings, each 1.3 m long. __________ metres
 
b)
Palings cost $1.25 each.
 
How much would 46 palings cost? $ __________ . __________
Task administration: 
This task is completed with pencil and paper only.
Level:
4
Curriculum info: 
Maths, Number and Algebra, Number Strategies
Keywords: 
multiplication, decimals, money
Description of task: 
Students carry out calculations involving multiplication of whole numbers by decimal numbers.
Curriculum Links: 
 
This resource can help to identify students' ability to apply additive or multiplicative strategies flexibly to whole numbers, ratios and equivalent fractions (including decimals and percentages) to solve multiplication problems.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Multiplicative thinking, sets 6-7
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
  Y9 (04/1999)
a) i)
ii)
iii)		 8.4
14.4
59.8		 very easy
very easy
easy
b)    $57.50 [accept $57.5] easy
Diagnostic and formative information: 
   Common error Likely calculation Likely reason
a) i)
    ii)
    iii)		 84
144
598		    Incorrect magnitude of answer because decimal point was ignored (possible place value error).
a) ii) 18.12 6 × 2 = 12
6 × 4 = .24		 Incorrect use of vertical algorithm.