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Reef and Granny

Stage: 2 Challenge Level: Challenge Level:1

James from Blue Mountains Grammar School said:

I think the best knot to make things secure is the reef knot. Why I thought that way is because the blue string is tied on the red string and the red is tied on the blue. So it will not disconnect under any circumstances unless you cut them or manually disconnect them.

I can see exactly what you mean, James. Alex from Hutchins School agreed with James:

I think the reef knot is the best because it stays in the same shape and so it will be less likely to slip.

Raj and Tom from Norfolk House School added:

The reef knot is strongest because the harder you pull the tighter the knot gets.

Natasha and Katy from Banbury School thought that the fact that the reef knot is flatter than the granny knot might make a difference too.

Phillip from the Hutchins Junior School thought that the conditions might make a difference too. He decided that:

A reef knot is much better when it is wet because a lubricant will keep it strong with friction and the knot's two parts will stay together, whereas a granny knot will not have the two intertwined parts.

These are good reasons, well done.


The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities can be found here.
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NRICH is part of the family of activities in the Millennium Mathematics Project.