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## 'Magic Plant' printed from http://nrich.maths.org/

Lots of you sent in your solutions to this
problem - unfortunately far too many to mention everyone. Most of
you worked out the plant's height each day, which is a very good
way of approaching the problem. Here is an example of this method
from Tom who goes to Linden Primary School:

So first you start with 2 centimetres.

On Saturday it's double 2. And double 2 is 4.

On Sunday is's double 4. And double 4 is 8.

On Monday it's double 8. And double 8 is 16.

So the answer is ...16 centimetres.

This is very clearly recorded - well
done Tom. Hannah, Grace and Ellie, who were attending Royal
Institution masterclasses, sent a very similar solution. So did
Oliver from Webbers School, Livvy (who didn't say which school she
is from) and someone from St Joseph's School in Harrogate. Ha Young
from Wesley College wrote down the same calculations in a slightly
different way, showing that doubling means multiplying by
two:

On Friday at 9am, it was 2cm

On Saturday at 9am, it was 2x2=4cm

On Sunday at 9am, it was 2x2x2=8cm

On Monday at 9am, it was 2x2x2x2=16cm

So, the answer is 16cm.

Some pupils from Queens Crescent School also
wrote down something a little different. Rather than recording
multiplication, they representated the calculations as addition,
like this:

2+2=4

4+4=8

8+8=16

Answer=16

In other words, doubling a number, or
multiplying it by two, is the same as adding it to itself. Very
well done all of you.