Addition and subtraction

  • No Square Sums
    problem

    No Square Sums

    Age
    14 to 16
    Challenge level

    How many numbers do you need to remove to avoid making a perfect square?

  • Small tomato seedlings in pink pots.
    problem

    Digit Sum

    Age
    14 to 16
    Challenge level

    What is the sum of all the digits in all the integers from one to one million?

  • Small tomato seedlings in pink pots.
    problem

    Three Primes

    Age
    14 to 16
    Challenge level

    Weekly Problem 6 - 2010
    Can you find three primes such that their product is exactly five times their sum? Do you think you have found all possibilities?

  • Magic squares for special occasions
    article

    Magic Squares for Special Occasions

    This article explains how to make your own magic square to mark a special occasion with the special date of your choice on the top line.
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