Explaining, convincing and proving

  • Repetitiously
    problem
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    Repetitiously

    Age
    14 to 16
    Challenge level
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    Can you express every recurring decimal as a fraction?

  • Terminology
    problem
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    Terminology

    Age
    14 to 16
    Challenge level
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    Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?

  • Semi-detached
    problem
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    Semi-detached

    Age
    14 to 16
    Challenge level
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    A square of area 40 square cms is inscribed in a semicircle. Find the area of the square that could be inscribed in a circle of the same radius.

  • Ordered Sums
    problem

    Ordered sums

    Age
    14 to 16
    Challenge level
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    Let a(n) be the number of ways of expressing the integer n as an ordered sum of 1's and 2's. Let b(n) be the number of ways of expressing n as an ordered sum of integers greater than 1. (i) Calculate a(n) and b(n) for n<8. What do you notice about these sequences? (ii) Find a relation between a(p) and b(q). (iii) Prove your conjectures.

  • problem
    Favourite

    Triangles and petals

    Age
    14 to 16
    Challenge level
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    An equilateral triangle rotates around regular polygons and produces an outline like a flower. What are the perimeters of the different flowers?

  • Inscribed in a Circle
    problem
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    Inscribed in a circle

    Age
    14 to 16
    Challenge level
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    The area of a square inscribed in a circle with a unit radius is 2. What is the area of these other regular polygons inscribed in a circle with a unit radius?

  • Painted Cube
    problem
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    Painted cube

    Age
    14 to 16
    Challenge level
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    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?

  • The Spider and the Fly
    problem
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    The spider and the fly

    Age
    14 to 16
    Challenge level
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    A spider is sitting in the middle of one of the smallest walls in a room and a fly is resting beside the window. What is the shortest distance the spider would have to crawl to catch the fly?

  • Multiplication square
    problem
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    Multiplication square

    Age
    14 to 16
    Challenge level
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    Pick a square within a multiplication square and add the numbers on each diagonal. What do you notice?

  • Triangle in a Triangle
    problem
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    Triangle in a triangle

    Age
    14 to 16
    Challenge level
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    Can you work out the fraction of the original triangle that is covered by the inner triangle?