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  #### Resources tagged with Mathematical reasoning & proof similar to One, Three, Five, Seven:
  
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  ### There are 162 results
  
  Broad Topics > Using, Applying and Reasoning about Mathematics > Mathematical reasoning & proof
  
  ### The Triangle Game
  
  ##### Age 11 to 16 Challenge Level:
  
  Can you discover whether this is a fair game?
  
  ##### Age 7 to 14 Challenge Level:
  
  I added together some of my neighbours house numbers. Can you explain the patterns I noticed?
  
  ### Go Forth and Generalise
  
  ##### Age 11 to 14
  
  Spotting patterns can be an important first step - explaining why it is appropriate to generalise is the next step, and often the most interesting and important.
  
  ### Yih or Luk Tsut K'i or Three Men's Morris
  
  ##### Age 11 to 18 Challenge Level:
  
  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. . . .
  
  ### Tessellating Hexagons
  
  ##### Age 11 to 14 Challenge Level:
  
  Which hexagons tessellate?
  
  ### Concrete Wheel
  
  ##### Age 11 to 14 Challenge Level:
  
  A huge wheel is rolling past your window. What do you see?
  
  ### Chocolate Maths
  
  ##### Age 11 to 14 Challenge Level:
  
  Pick the number of times a week that you eat chocolate. This number must be more than one but less than ten. Multiply this number by 2. Add 5 (for Sunday). Multiply by 50... Can you explain why it. . . .
  
  ### How Many Dice?
  
  ##### Age 11 to 14 Challenge Level:
  
  A standard die has the numbers 1, 2 and 3 are opposite 6, 5 and 4 respectively so that opposite faces add to 7? If you make standard dice by writing 1, 2, 3, 4, 5, 6 on blank cubes you will find. . . .
  
  ##### Age 11 to 14 Challenge Level:
  
  A little bit of algebra explains this 'magic'. Ask a friend to pick 3 consecutive numbers and to tell you a multiple of 3. Then ask them to add the four numbers and multiply by 67, and to tell you. . . .
  
  ### Clocked
  
  ##### Age 11 to 14 Challenge Level:
  
  Is it possible to rearrange the numbers 1,2......12 around a clock face in such a way that every two numbers in adjacent positions differ by any of 3, 4 or 5 hours?
  
  ### Königsberg
  
  ##### Age 11 to 14 Challenge Level:
  
  Can you cross each of the seven bridges that join the north and south of the river to the two islands, once and once only, without retracing your steps?
  
  ### One O Five
  
  ##### Age 11 to 14 Challenge Level:
  
  You can work out the number someone else is thinking of as follows. Ask a friend to think of any natural number less than 100. Then ask them to tell you the remainders when this number is divided by. . . .
  
  ### More Number Pyramids
  
  ##### Age 11 to 14 Challenge Level:
  
  When number pyramids have a sequence on the bottom layer, some interesting patterns emerge...
  
  ### Konigsberg Plus
  
  ##### Age 11 to 14 Challenge Level:
  
  Euler discussed whether or not it was possible to stroll around Koenigsberg crossing each of its seven bridges exactly once. Experiment with different numbers of islands and bridges.
  
  ### Tourism
  
  ##### Age 11 to 14 Challenge Level:
  
  If you can copy a network without lifting your pen off the paper and without drawing any line twice, then it is traversable. Decide which of these diagrams are traversable.
  
  ### Disappearing Square
  
  ##### Age 11 to 14 Challenge Level:
  
  Do you know how to find the area of a triangle? You can count the squares. What happens if we turn the triangle on end? Press the button and see. Try counting the number of units in the triangle now. . . .
  
  ### Sticky Numbers
  
  ##### Age 11 to 14 Challenge Level:
  
  Can you arrange the numbers 1 to 17 in a row so that each adjacent pair adds up to a square number?
  
  ### Triangle Inequality
  
  ##### Age 11 to 14 Challenge Level:
  
  ABC is an equilateral triangle and P is a point in the interior of the triangle. We know that AP = 3cm and BP = 4cm. Prove that CP must be less than 10 cm.
  
  ### Convex Polygons
  
  ##### Age 11 to 14 Challenge Level:
  
  Show that among the interior angles of a convex polygon there cannot be more than three acute angles.
  
  ### More Number Sandwiches
  
  ##### Age 11 to 16 Challenge Level:
  
  When is it impossible to make number sandwiches?
  
  ### Dicing with Numbers
  
  ##### Age 11 to 14 Challenge Level:
  
  In how many ways can you arrange three dice side by side on a surface so that the sum of the numbers on each of the four faces (top, bottom, front and back) is equal?
  
  ### Problem Solving, Using and Applying and Functional Mathematics
  
  ##### Age 5 to 18 Challenge Level:
  
  Problem solving is at the heart of the NRICH site. All the problems give learners opportunities to learn, develop or use mathematical concepts and skills. Read here for more information.
  
  ### 9 Weights
  
  ##### Age 11 to 14 Challenge Level:
  
  You have been given nine weights, one of which is slightly heavier than the rest. Can you work out which weight is heavier in just two weighings of the balance?
  
  ### Picture Story
  
  ##### Age 14 to 16 Challenge Level:
  
  Can you see how this picture illustrates the formula for the sum of the first six cube numbers?
  
  ### Dalmatians
  
  ##### Age 14 to 18 Challenge Level:
  
  Investigate the sequences obtained by starting with any positive 2 digit number (10a+b) and repeatedly using the rule 10a+b maps to 10b-a to get the next number in the sequence.
  
  ### Janine's Conjecture
  
  ##### Age 14 to 16 Challenge Level:
  
  Janine noticed, while studying some cube numbers, that if you take three consecutive whole numbers and multiply them together and then add the middle number of the three, you get the middle number. . . .
  
  ### Adding All Nine
  
  ##### Age 11 to 14 Challenge Level:
  
  Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some. . . .
  
  ### Eleven
  
  ##### Age 11 to 14 Challenge Level:
  
  Replace each letter with a digit to make this addition correct.
  
  ### Proofs with Pictures
  
  ##### Age 14 to 18
  
  Some diagrammatic 'proofs' of algebraic identities and inequalities.
  
  ### Natural Sum
  
  ##### Age 14 to 16 Challenge Level:
  
  The picture illustrates the sum 1 + 2 + 3 + 4 = (4 x 5)/2. Prove the general formula for the sum of the first n natural numbers and the formula for the sum of the cubes of the first n natural. . . .
  
  ### Cosines Rule
  
  ##### Age 14 to 16 Challenge Level:
  
  Three points A, B and C lie in this order on a line, and P is any point in the plane. Use the Cosine Rule to prove the following statement.
  
  ### Picturing Pythagorean Triples
  
  ##### Age 14 to 18
  
  This article discusses how every Pythagorean triple (a, b, c) can be illustrated by a square and an L shape within another square. You are invited to find some triples for yourself.
  
  ### Impossible Sandwiches
  
  ##### Age 11 to 18
  
  In this 7-sandwich: 7 1 3 1 6 4 3 5 7 2 4 6 2 5 there are 7 numbers between the 7s, 6 between the 6s etc. The article shows which values of n can make n-sandwiches and which cannot.
  
  ### Calendar Capers
  
  ##### Age 11 to 14 Challenge Level:
  
  Choose any three by three square of dates on a calendar page...
  
  ### Pattern of Islands
  
  ##### Age 11 to 14 Challenge Level:
  
  In how many distinct ways can six islands be joined by bridges so that each island can be reached from every other island...
  
  ### Children at Large
  
  ##### Age 11 to 14 Challenge Level:
  
  There are four children in a family, two girls, Kate and Sally, and two boys, Tom and Ben. How old are the children?
  
  ### Matter of Scale
  
  ##### Age 14 to 16 Challenge Level:
  
  Prove Pythagoras' Theorem using enlargements and scale factors.
  
  ### Unit Interval
  
  ##### Age 14 to 18 Challenge Level:
  
  Take any two numbers between 0 and 1. Prove that the sum of the numbers is always less than one plus their product?
  
  ### Sprouts Explained
  
  ##### Age 7 to 18
  
  This article invites you to get familiar with a strategic game called "sprouts". The game is simple enough for younger children to understand, and has also provided experienced mathematicians with. . . .
  
  ### Multiplication Square
  
  ##### Age 14 to 16 Challenge Level:
  
  Pick a square within a multiplication square and add the numbers on each diagonal. What do you notice?
  
  ### The Great Weights Puzzle
  
  ##### Age 14 to 16 Challenge Level:
  
  You have twelve weights, one of which is different from the rest. Using just 3 weighings, can you identify which weight is the odd one out, and whether it is heavier or lighter than the rest?
  
  ### A Long Time at the Till
  
  ##### Age 14 to 18 Challenge Level:
  
  Try to solve this very difficult problem and then study our two suggested solutions. How would you use your knowledge to try to solve variants on the original problem?
  
  ### Advent Calendar 2011 - Secondary
  
  ##### Age 11 to 18 Challenge Level:
  
  Advent Calendar 2011 - a mathematical activity for each day during the run-up to Christmas.
  
  ### Triangular Intersection
  
  ##### Age 14 to 16 Short Challenge Level:
  
  What is the largest number of intersection points that a triangle and a quadrilateral can have?
  
  ### Proof Sorter - Quadratic Equation
  
  ##### Age 14 to 18 Challenge Level:
  
  This is an interactivity in which you have to sort the steps in the completion of the square into the correct order to prove the formula for the solutions of quadratic equations.
  
  ### Top-heavy Pyramids
  
  ##### Age 11 to 14 Challenge Level:
  
  Use the numbers in the box below to make the base of a top-heavy pyramid whose top number is 200.
  
  ### Tower of Hanoi
  
  ##### Age 11 to 14 Challenge Level:
  
  The Tower of Hanoi is an ancient mathematical challenge. Working on the building blocks may help you to explain the patterns you notice.
  
  ### AMGM
  
  ##### Age 14 to 16 Challenge Level:
  
  Can you use the diagram to prove the AM-GM inequality?
  
  ### Always the Same
  
  ##### Age 11 to 14 Challenge Level:
  
  Arrange the numbers 1 to 16 into a 4 by 4 array. Choose a number. Cross out the numbers on the same row and column. Repeat this process. Add up you four numbers. Why do they always add up to 34?
  
  ### Aba
  
  ##### Age 11 to 14 Challenge Level:
  
  In the following sum the letters A, B, C, D, E and F stand for six distinct digits. Find all the ways of replacing the letters with digits so that the arithmetic is correct.