Charging the car

Charging the car

Pencil and paper
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about working out costs for charging an electric car.

illustration: car charging station showing 91.9 cents per KWh

The battery of Mrs Henare's electric car holds 40 KWh (kilowatt-hours) of energy.

One KWh costs 91.9 cents.

 

a) If Mrs Henare's battery already had 15 KWh of energy, how much would it cost to fully charge it?
 
$ __________
 
b) Mrs Henare noticed that she had used three-quarters of her charge. How much will it cost her to fully charge the battery?
 
$ __________
 
c) If Mrs Henare then used $18.38 worth of energy from the full battery, how many KWh would she have left?
 
__________ KWh
Task administration: 
This task is completed with pencil and paper only.
Level:
5
Curriculum info: 
Maths, Number and Algebra, Number Strategies
Keywords: 
rates, money
Description of task: 
The price of various amounts of diesel is required given its price per litre as well as writing out how much diesel can be bought for a given price.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Multiplicative thinking, sets 8-9
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
  

Y9 (05/1997)

Y10 (05/1997)
a) $22.98 [$22.975 rounded, accept $22.95 - $23.00] difficult moderate
b) $27.57 [Accept $27.55 - $27.60] very difficult difficult
c) 20 very difficult moderate
Diagnostic and formative information: 
    Student response Likely calculation Likely misconception
a) $22.75 25 × .91 Uses price of 91c instead of 91.9c.
b)
b)		 $9.19
$27.50		 10 × .919 Finds the cost of 1/4 tank (not 3/4).
Rounds answer to nearest 10c.
c) 21.62 40 - 18.38 Subtracts money from litres.