
Pumpkin patch

Seega

Alquerque

Introducing NRICH TWILGO

Like a circle in a spiral


Clocking off

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

Prime magic

Air nets

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?

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

Sprouts

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?

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

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.

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



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?

Charting success

Charting more success

What is the question?

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

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?


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

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.


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?

Triangles in the middle


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?

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.

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?

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.

Pyramidal n-gon

Always perfect
Show that if you add 1 to the product of four consecutive numbers the answer is ALWAYS a perfect square.

Summing squares

Semicircular design
The diagram to the right shows a logo made from semi-circular arcs. What fraction of the logo is shaded?

Salinon
This shape comprises four semi-circles. What is the relationship between the area of the shaded region and the area of the circle on AB as diameter?


One and three

Factorising with multilink
Can you find out what is special about the dimensions of rectangles you can make with squares, sticks and units?

A tilted square
The opposite vertices of a square have coordinates (a,b) and (c,d). What are the coordinates of the other vertices?

A question of scale
Use your skill and knowledge to place various scientific lengths in order of size. Can you judge the length of objects with sizes ranging from 1 Angstrom to 1 million km with no wrong attempts?

In or out?
Four arcs are drawn in a circle to create a shaded area. What fraction of the area of the circle is shaded?

Triangles and petals
An equilateral triangle rotates around regular polygons and produces an outline like a flower. What are the perimeters of the different flowers?

Travelling by train

Platonic planet

Sliced

Plus minus
Can you explain the surprising results Jo found when she calculated the difference between square numbers?

Nicely similar
If the hypotenuse (base) length is 100cm and if an extra line splits the base into 36cm and 64cm parts, what were the side lengths for the original right-angled triangle?

Fill me up too
In Fill Me Up we invited you to sketch graphs as vessels are filled with water. Can you work out the equations of the graphs?



Trisected triangle
Four tiles are given. For which of them can three be placed together to form an equilateral triangle?

Pair products
Choose four consecutive whole numbers. Multiply the first and last numbers together. Multiply the middle pair together. What do you notice?

Oldest and youngest

Circuit training

Sitting pretty
A circle of radius r touches two sides of a right angled triangle, sides x and y, and has its centre on the hypotenuse. Can you prove the formula linking x, y and r?

Dating made easier
If a sum invested gains 10% each year how long before it has doubled its value?

Spotting the loophole
A visualisation problem in which you search for vectors which sum to zero from a jumble of arrows. Will your eyes be quicker than algebra?


Jam
To avoid losing think of another very well known game where the patterns of play are similar.

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

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

Just rolling round

Perfectly square
The sums of the squares of three related numbers is also a perfect square - can you explain why?



Something in common

Facial sums

Gutter
Manufacturers need to minimise the amount of material used to make their product. What is the best cross-section for a gutter?

Making tracks


Wari

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

Coke machine

Changing places

Tennis training

3D treasure hunt
Some treasure has been hidden in a three-dimensional grid! Can you work out a strategy to find it as efficiently as possible?


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?

Attractive tablecloths
Charlie likes tablecloths that use as many colours as possible, but insists that his tablecloths have some symmetry. Can you work out how many colours he needs for different tablecloth designs?

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


Just opposite

Painted cube
Imagine a large cube made from small red cubes being dropped into a pot of yellow paint. How many of the small cubes will have yellow paint on their faces?

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

Slippage
