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Inside Triangles

Age 5 to 7
Challenge Level Yellow star
Primary curriculum
  • Problem
  • Getting Started
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Shree from the International School Frankfurt in Germany sent in these solutions in which triangles in different places were explored:

  
 


Neptune Class from Riverley Primary wrote to say:

We think that there are 6 triangles in total.

We made sure that each triangle was a different type (scalene, isosceles, right-angled and equilateral) and we experimented with different shapes on the pin-board.
We thought that there must also be a mathematical way to systematically calculate the solution to the problem, but we're still working on it.

I think there are a few more than six triangles, but I like the way you thought that working systematically would help. 

That's exactly what Greg from Swanland County Primary School did.  He said:

First I tried to just make triangles with a dot inside.

 

Then I tried ones with a four dot base.

 

Then I tried one with a two dot base.

 


I think there are 7 different triangles.
 

We had a solution come in from Lily-Mai and Dillon from Millbrook School in Swindon. Their teacher wrote to say that they think they have found all nine triangles, and would love to see their solution on the NRICH website! We agree with Lily-Mai and Dillon - there are nine different triangles. They worked systematically, finding all triangles with a base of 2, then 3, then 4:


These show some very good approaches.  Thank you for sending them into us.

Some of you might like to explore further, being curious about what having two dots within the triangles would be like, for example.

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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.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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