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'Reef and Granny' printed from http://nrich.maths.org/

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This is a reef knot:

reef knot



And this is a granny knot:

granny knot


Before you read any further, it might be a good idea to make a reef knot and a granny knot. You do not need coloured string - it can even be done with shoelaces!

Can you see any differences between them?

When a reef knot is pulled tight it looks like this:

reef knot pulled tight


When a granny knot is pulled tight it looks like this:

granny pulled tight 1


... or this:

granny pulled tight 2


or this:

granny pulled tight 3


Which do you think is the best knot for making things secure?

Why?