Get students applying their knowledge of multiplying and dividing decimals and working with units of length in this fun video-based Maths challenge.

Note - You'll need access to the internet and YouTube to show video 1, video 2 and video 3 for this lesson. You could easily fit this into a 40-60 minute lesson, depending on students' level and extension questions.

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‍Question: How many books do you need to make a human stack of books?

‍Australian Curriculum links

• Multiply and divide fractions and decimals using efficient written strategies and digital technologies (ACMNA154 - Scootle )
• Recognise and solve problems involving simple ratios (ACMNA173 - Scootle )
• Draw different views of prisms and solids formed from combinations of prisms (ACMMG161 - Scootle )

Relevant Edrolo Year 7 Maths lessons

• 5E Multiplying with decimals 
• 5F Dividing with decimals 
• 9A Units of length 
• 9D Drawing 3D objects 

How to implement in your class

• Google form 
• Jamboard 
• Powerpoint 
• groups/ partners/ individual work  
• Whiteboards/ big paper to brainstorm 
• Students write a hypothesis, method, results, discuss/ present their conclusion to the class/ partners/ groups   

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Part 1 - Setting the problem

Show students video 1. The video shows me (Rebecca) next to books that are being stacked one by one.

Teacher Questions

• What is an overestimate? 
• What is an underestimate? 
• What information is useful in this video? 
• What information do you need to solve this problem?

Students are: 

• Guessing estimates 
• Reasoning: Apply known geometric facts to draw conclusions about shapes
• Problem Solving: Formulating and solving authentic problems involving numbers and measurement
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Part 2 - Solving the problem

Show students video 2. The video shows that Rebecca is 165 cm tall. The length x width x height of the book is 29.8 x 22 cm x 1.9 cm. 

Teacher Questions

• How could you solve this problem? 
• Would you round your calculation up or down? 

Students are: 

• Reasoning: Apply known geometric facts to draw conclusions about shapes
• Problem Solving: Formulating and solving authentic problems involving numbers and measurement

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Part 3 - Answer and exploration

Show students video 3. The books are counted on screen and the final number that appears is 87. 

Teacher Questions: 

• Did your answer match the video? 
• Why was your result the same/ different? 

Students are: 

• Reasonsing: Students are drawing conclusions about their calculations
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Extension

• What would be the total number of books if the books were stacked standing up as opposed to laying down? 
• How would the height of the books be affected if the books were not rotated 180 degrees when stacked? 
• If Rebecca wore a headband that increased her height by 11 cm, how many more books are needed to reach her height? 
• Half of the books are stacked - what is this number? 
• 30% of the books are stacked, what is this number? 
• If Rebecca wore a headband and the total book count was 92 books, how high is her headband? 
• The rate that it takes to stack the books is 1 book per 20 seconds. How long would it take to stack 87 books? 
• The total time it took to stack 87 books took 42 minutes, what would attribute to the extra time?