
Introducing NRICH TWILGO

Pumpkin patch

Seega

Alquerque

Prime magic

Like a circle in a spiral

Fruity totals
In this interactivity each fruit has a hidden value. Can you deduce what each one is worth?


Air nets

Clocking off

Wipeout
Can you do a little mathematical detective work to figure out which number has been wiped out?

Ding dong bell

Take three from five
Caroline and James pick sets of five numbers. Charlie tries to find three that add together to make a multiple of three. Can they stop him?


Charting success

Charting more success

What is the question?


Yih or Luk tsut k'i or Three Men's Morris
Some puzzles requiring no knowledge of knot theory, just a careful inspection of the patterns. A glimpse of the classification of knots and a little about prime knots, crossing numbers and knot arithmetic.

Spots and measles
99% of people who have measles have spots. Ben has spots. Do you think he has measles?

Shaping the universe I - planet Earth
This article explores ths history of theories about the shape of our planet. It is the first in a series of articles looking at the significance of geometric shapes in the history of astronomy.

Sprouts

Shaping the universe II - the solar system
The second in a series of articles on visualising and modelling shapes in the history of astronomy.


Shaping the universe III - to infinity and beyond
The third installment in our series on the shape of astronomical systems, this article explores galaxies and the universe beyond our solar system.

Marbles in a box
How many winning lines can you make in a three-dimensional version of noughts and crosses?

Triangles in the middle


Hamiltonian cube
Find the length along the shortest path passing through certain points on the cube.


Instant insanity
Given the nets of 4 cubes with the faces coloured in 4 colours, build a tower so that on each vertical wall no colour is repeated, that is all 4 colours appear.

Funny factorisation
Using the digits 1 to 9, the number 4396 can be written as the product of two numbers. Can you find the factors?

Charlie's delightful machine
Here is a machine with four coloured lights. Can you develop a strategy to work out the rules controlling each light?

Triangle in a trapezium
Can you find and prove the relationship between the area of a trapezium and the area of a triangle constructed within it?

Nine colours
Can you use small coloured cubes to make a 3 by 3 by 3 cube so that each face of the bigger cube contains one of each colour?

What's it worth?
There are lots of different methods to find out what the shapes are worth - how many can you find?

The bridges of Konigsberg
Investigate how networks can be used to solve a problem for the 18th Century inhabitants of Konigsberg.

Searching for mean(ing)
If you have a large supply of 3kg and 8kg weights, how many of each would you need for the average (mean) of the weights to be 6kg?

Sliding puzzle

LOGO challenge - circles as animals
See if you can anticipate successive 'generations' of the two animals shown here.



LOGO challenge - triangles-squares-stars
Can you recreate these designs? What are the basic units? What movement is required between each unit? Some elegant use of procedures will help - variables not essential.

A problem of time

Immersion
Various solids are lowered into a beaker of water. How does the water level rise in each case?

Triangles within squares

Perception versus reality
Infographics are a powerful way of communicating statistical information. Can you come up with your own?


Terminology
Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?

Facial sums

Making tracks

All tied up


Hypotenuse lattice points

At right angles
Can you decide whether two lines are perpendicular or not? Can you do this without drawing them?

Triangles within pentagons

Iff
Take a triangular number, multiply it by 8 and add 1. What is special about your answer? Can you prove it?

Tennis training


Bendy quad
Four rods are hinged at their ends to form a convex quadrilateral. Investigate the different shapes that the quadrilateral can take. Be patient this problem may be slow to load.

One out one under

Which list is which?
Six samples were taken from two distributions but they got muddled up. Can you work out which list is which?

Star gazing

Curvy areas
Have a go at creating these images based on circles. What do you notice about the areas of the different sections?



Tetra square

Mystic rose
Use the animation to help you work out how many lines are needed to draw mystic roses of different sizes.

Pick's theorem
Polygons drawn on square dotty paper have dots on their perimeter (p) and often internal (i) ones as well. Find a relationship between p, i and the area of the polygons.


Contact

The perforated cube

Out of the window

Penta colour

Building gnomons


Quadratic patterns
Surprising numerical patterns can be explained using algebra and diagrams...

Concrete calculation

Slick summing
Watch the video to see how Charlie works out the sum. Can you adapt his method?



Corridors

Packing boxes

Picture story
Can you see how this picture illustrates the formula for the sum of the first six cube numbers?

Negatively triangular
How many intersections do you expect from four straight lines ? Which three lines enclose a triangle with negative co-ordinates for every point ?


Escalator

Pythagoras perimeters
If you know the perimeter of a right angled triangle, what can you say about the area?

Painted purple

When the angles of a triangle don't add up to 180 degrees

Hexy-metry
A hexagon, with sides alternately a and b units in length, is inscribed in a circle. How big is the radius of the circle?

Newspaper sheets

Proximity
We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.

Bus stop

Steel cables
Some students have been working out the number of strands needed for different sizes of cable. Can you make sense of their solutions?


Cubic covering

Tilting triangles

Partly painted cube
Jo made a cube from some smaller cubes, painted some of the faces of the large cube, and then took it apart again. 45 small cubes had no paint on them at all. How many small cubes did Jo use?

Speed-time problems at the Olympics
Have you ever wondered what it would be like to race against Usain Bolt?