Explaining, convincing and proving

  • Triangle Incircle Iteration
    problem

    Triangle Incircle Iteration

    Age
    14 to 16
    Challenge level
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    Keep constructing triangles in the incircle of the previous triangle. What happens?

  • Diophantine n-tuples
    problem

    Diophantine N-Tuples

    Age
    14 to 16
    Challenge level
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    Can you explain why a sequence of operations always gives you perfect squares?

  • DOTS Division
    problem

    DOTS Division

    Age
    14 to 16
    Challenge level
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    Take any pair of two digit numbers x=ab and y=cd where, without loss of generality, ab > cd . Form two 4 digit numbers r=abcd and s=cdab and calculate: {r^2 - s^2} /{x^2 - y^2}.

  • No Right Angle Here
    problem

    No Right Angle Here

    Age
    14 to 16
    Challenge level
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    Prove that the internal angle bisectors of a triangle will never be perpendicular to each other.

  • Fixing the Odds
    problem

    Fixing the Odds

    Age
    14 to 16
    Challenge level
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    You have two bags, four red balls and four white balls. You must put all the balls in the bags although you are allowed to have one bag empty. How should you distribute the balls between the two bags so as to make the probability of choosing a red ball as small as possible and what will the probability be in that case?

  • The Pillar of Chios
    problem

    The Pillar of Chios

    Age
    14 to 16
    Challenge level
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    Semicircles are drawn on the sides of a rectangle. Prove that the sum of the areas of the four crescents is equal to the area of the rectangle.

  • Encircling
    problem

    Encircling

    Age
    14 to 16
    Challenge level
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    An equilateral triangle is sitting on top of a square. What is the radius of the circle that circumscribes this shape?

  • Cyclic Quad Jigsaw
    problem

    Cyclic Quad Jigsaw

    Age
    14 to 16
    Challenge level
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    A picture is made by joining five small quadrilaterals together to make a large quadrilateral. Is it possible to draw a similar picture if all the small quadrilaterals are cyclic?

  • AMGM
    problem

    AMGM

    Age
    14 to 16
    Challenge level
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    Can you use the diagram to prove the AM-GM inequality?

  • Similarly so
    problem

    Similarly So

    Age
    14 to 16
    Challenge level
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    ABCD is a square. P is the midpoint of AB and is joined to C. A line from D perpendicular to PC meets the line at the point Q. Prove AQ = AD.