Skip over navigation
Cambridge University Faculty of Mathematics NRich logo
menu search
  • Teachers expand_more
    • Early years
    • Primary
    • Secondary
    • Post-16
    • Events
    • Professional development
  • Students expand_more
    • Primary
    • Secondary
    • Post-16
  • Parents expand_more
    • Early Years
    • Primary
    • Secondary
    • Post-16
  • Problem-Solving Schools
  • About NRICH expand_more
    • About us
    • Impact stories
    • Support us
    • Our funders
    • Contact us
  • search

Or search by topic

Number and algebra

  • The Number System and Place Value
  • Calculations and Numerical Methods
  • Fractions, Decimals, Percentages, Ratio and Proportion
  • Properties of Numbers
  • Patterns, Sequences and Structure
  • Algebraic expressions, equations and formulae
  • Coordinates, Functions and Graphs

Geometry and measure

  • Angles, Polygons, and Geometrical Proof
  • 3D Geometry, Shape and Space
  • Measuring and calculating with units
  • Transformations and constructions
  • Pythagoras and Trigonometry
  • Vectors and Matrices

Probability and statistics

  • Handling, Processing and Representing Data
  • Probability

Working mathematically

  • Thinking mathematically
  • Developing positive attitudes
  • Cross-curricular contexts

Advanced mathematics

  • Decision Mathematics and Combinatorics
  • Advanced Probability and Statistics
  • Mechanics
  • Calculus

For younger learners

  • Early Years Foundation Stage

Fractional Triangles

Age 7 to 11
Challenge Level Yellow star
Primary curriculum
  • Problem
  • Getting Started
  • Student Solutions
  • Teachers' Resources

Chris and Jenny sent us some colourful diagrams to show their answers:

Two halvesThree thirdsSix sixthsNine ninths

Julia drew on the line she'd draw to get quarters. Can you see that there are now four identical triangles? (Concentrate on the thickest lines.)
 
 
Four quarters


However, Anna wrote to say:
The least amount of line needed is one line dividing the central two triangles of the square in half.

I knew that the diagram had 18 triangles which is a number not divisible by 4. So I divided two triangles in half to have a total of 20 triangles which is a number divisible by 4.  At first I drew the smaller triangles at the side of the square but this did not work.  Then I divided all of the triangles in half using 9 lines giving me 36 triangles.  I successfully divided the diagram into equally sized quarters of the same shape, but this did not give me the smallest amount of line.  Once more I split two triangles in half but this time the halved triangle was in the middle.
 
There are lots of ways to divide the shape up into two halves. Sunita and Raj sent us two that they thought were nice:
 
 
Two halvesTwo halves

The Maths Challenge Group at St Aidan's VC School also sent us some different ways of dividing the shape into two halves.  Here are the images they sent:



They told us:

We all compared our answers and came up with these as our final results. We looked very carefully at  5 and 7, 3 and 6 in order to be sure that they were different answers not merely a rotation. We are happy with our results after our discussion.

Thank you for sharing that with us and well done everyone.

You may also like

Chocolate

There are three tables in a room with blocks of chocolate on each. Where would be the best place for each child in the class to sit if they came in one at a time?

Four Triangles Puzzle

Cut four triangles from a square as shown in the picture. How many different shapes can you make by fitting the four triangles back together?

Cut it Out

Can you dissect an equilateral triangle into 6 smaller ones? What number of smaller equilateral triangles is it NOT possible to dissect a larger equilateral triangle into?

  • Tech help
  • Accessibility Statement
  • Sign up to our newsletter
  • Twitter X logo

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.

University of Cambridge logo NRICH logo