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Magic Plant

Stage: 1 Challenge Level: Challenge Level:2 Challenge Level:2

Magic Plant


On Friday at $9$ am, the magic plant was only $2$ centimetres tall.



Every twenty four hours, it doubled its height.
How tall was it on Monday at $9$ am?

Why do this problem?

This problem offers learners a context in which to practise doubling. It also gives children the opportunity to choose their own representation and recording methods.

Possible approach

You could start by asking children a different question, for example, imagining a magic plant that grows one centimetre every day. Explain that you are particularly looking out for what they choose to write down or do and offer them use of anything in the classroom that they feel would be helpful. Once they have had a go at this introductory task, share some of the different representations they have made, making it clear that all of them have value and that each of us finds different things useful.

Then introduce the problem itself and again, leave children to work on it, perhaps in pairs. When you share their work this time, it will be interesting to see which children adopt a different form of representation than the one they used for the initial challenge. It might be worth finding out why some of them changed.

Key questions

How tall will the plant be on Saturday at 9am?
How tall will the plant be on Sunday at 9am?

Possible extension

Some children might like to predict the plant's height at later stages during the week as well before working it out. They may well be surprised at how quickly it grows!

Possible support

Some learners will find number line, number square or multiplication grid useful.