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.
Question: How many books do you need to make a human stack of books?
Australian Curriculum links
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
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
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
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 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? 
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