Making Maths: Triangular Ball

Stage: 2 Challenge Level: Challenge Level:1

Triangular ball
You will need:
  • Four or five sheets of stiff paper or thin card
  • Scissors
  • Pencil
  • Glue or stapler

What to do:
  1. Cut out 20 circles, all the same. (Make it easy for yourself - cut through two or three sheets of paper at the same time.)
  2. Fold three flaps in to make an equilateral triangle.

    To do this, first find the centre of the circle by folding it in half, then half again. Now fold one edge in to touch the centre. Fold another flap in to touch the centre AND make a point. Now fold the last flap in to the centre.
    Step 1
  3. Use this triangle to mark triangles on all the other circles and fold over all the flaps.
  4. Join (with paste or a staple) the flaps of five of the circles to make the top of the ball - like this:
    Step 2
    When you join the last flaps it will pull up into a sort of pyramid shape. Keep the flaps on the OUTSIDE.
  5. Join another five circles in the same way to make the bottom of the ball.
  6. Join the ten circles that are left in one long strip.
    Step 3
  7. Bend the strip around and join the end flaps - keep the flaps on the outside.
  8. Now join the top and bottom on to this strip - there's the ball!
This activity features in our December 2008 Advent Calendar .


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.