Addition and subtraction

  • Consecutive negative numbers
    problem
    Favourite

    Consecutive Negative Numbers

    Age
    11 to 14
    Challenge level

    Do you notice anything about the solutions when you add and/or subtract consecutive negative numbers?

  • A Connect Four game with red and yellow counters placed.
    problem
    Favourite

    Connect Three

    Age
    11 to 16
    Challenge level

    In this game the winner is the first to complete a row of three. Are some squares easier to land on than others?

  • Double Digit
    problem

    Double Digit

    Age
    11 to 14
    Challenge level
    Choose two digits and arrange them to make two double-digit numbers. Now add your double-digit numbers. Now add your single digit numbers. Divide your double-digit answer by your single-digit answer. Try lots of examples. What happens? Can you explain it?
  • Alphabet Soup
    problem

    Alphabet Soup

    Age
    11 to 14
    Challenge level
    This challenge is to make up YOUR OWN alphanumeric. Each letter represents a digit and where the same letter appears more than once it must represent the same digit each time.
  • As Easy as 1,2,3
    problem

    As Easy as 1,2,3

    Age
    11 to 14
    Challenge level
    When I type a sequence of letters my calculator gives the product of all the numbers in the corresponding memories. What numbers should I store so that when I type 'ONE' it returns 1, and when I type 'TWO' it returns 2, and so on.
  • Kids
    problem

    Kids

    Age
    11 to 14
    Challenge level
    Find the numbers in this sum
  • Machines
    problem

    Machines

    Age
    7 to 11
    Challenge level
    What is happening at each box in these machines?
  • Card Trick 2
    problem

    Card Trick 2

    Age
    11 to 14
    Challenge level
    Can you explain how this card trick works?
  • The Patent Solution
    problem

    The Patent Solution

    Age
    11 to 14
    Challenge level
    A combination mechanism for a safe comprises thirty-two tumblers numbered from one to thirty-two in such a way that the numbers in each wheel total 132... Could you open the safe?
  • Score
    problem

    Score

    Age
    11 to 14
    Challenge level
    There are exactly 3 ways to add 4 odd numbers to get 10. Find all the ways of adding 8 odd numbers to get 20. To be sure of getting all the solutions you will need to be systematic. What about a total of 15 with 6 odd numbers?
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