Indices

  • Multiplication Magic
    problem

    Multiplication magic

    Age
    14 to 16
    Challenge level
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    Given any 3 digit number you can use the given digits and name another number which is divisible by 37 (e.g. given 628 you say 628371 is divisible by 37 because you know that 6+3 = 2+7 = 8+1 = 9). The question asks you to explain the trick.
  • Lastly - well
    problem

    Lastly - well

    Age
    11 to 14
    Challenge level
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    What are the last two digits of 2^(2^2003)?
  • Powerful Factors
    problem

    Powerful factors

    Age
    16 to 18
    Challenge level
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    Use the fact that: x²-y² = (x-y)(x+y) and x³+y³ = (x+y) (x²-xy+y²) to find the highest power of 2 and the highest power of 3 which divide 5^{36}-1.
  • Pythagoras mod 5
    problem

    Pythagoras mod 5

    Age
    16 to 18
    Challenge level
    filled star filled star filled star
    Prove that for every right angled triangle which has sides with integer lengths: (1) the area of the triangle is even and (2) the length of one of the sides is divisible by 5.
  • Cube Roots
    problem

    Cube roots

    Age
    16 to 18
    Challenge level
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    Evaluate without a calculator: (5 sqrt2 + 7)^{1/3} - (5 sqrt2 - 7)^1/3}.
  • Sums of Squares
    problem

    Sums of squares

    Age
    16 to 18
    Challenge level
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    Can you prove that twice the sum of two squares always gives the sum of two squares?
  • Power Quady
    problem

    Power quady

    Age
    16 to 18
    Challenge level
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    Find all real solutions of the equation (x^2-7x+11)^(x^2-11x+30) = 1.
  • Really Mr. Bond
    problem

    Really Mr. Bond

    Age
    14 to 16
    Challenge level
    filled star filled star filled star

    115^2 = (110 x 120) + 25, that is 13225 895^2 = (890 x 900) + 25, that is 801025 Can you explain what is happening and generalise?

  • eNRICHing experience
    problem

    eNRICHing experience

    Age
    14 to 16
    Challenge level
    filled star empty star empty star

    Find the five distinct digits N, R, I, C and H in the following nomogram

  • Power Crazy
    problem

    Power crazy

    Age
    11 to 14
    Challenge level
    filled star filled star empty star
    What can you say about the values of n that make $7^n + 3^n$ a multiple of 10? Are there other pairs of integers between 1 and 10 which have similar properties?