Addition and subtraction

  • 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?

  • Cayley
    problem

    Cayley

    Age
    11 to 14
    Challenge level

    The letters in the following addition sum represent the digits 1 ... 9. If A=3 and D=2, what number is represented by "CAYLEY"?

  • Tis Unique
    problem

    Tis Unique

    Age
    11 to 14
    Challenge level

    This addition sum uses all ten digits 0, 1, 2...9 exactly once. Find the sum and show that the one you give is the only possibility.

  • And so on and so on
    problem

    And so on and so On

    Age
    11 to 14
    Challenge level

    If you wrote all the possible four digit numbers made by using each of the digits 2, 4, 5, 7 once, what would they add up to?

  • Largest Number
    problem

    Largest Number

    Age
    11 to 14
    Challenge level

    What is the largest number you can make using the three digits 2, 3 and 4 in any way you like, using any operations you like? You can only use each digit once.

  • Small tomato seedlings in pink pots.
    problem

    Negative Dice

    Age
    11 to 14
    Challenge level

    If the odd numbers on two dice are made negative, which of the totals cannot be achieved?

  • Multiply the Addition Square
    problem

    Multiply the Addition Square

    Age
    11 to 14
    Challenge level

    If you take a three by three square on a 1-10 addition square and multiply the diagonally opposite numbers together, what is the difference between these products. Why?

  • Small tomato seedlings in pink pots.
    problem

    Calculation 2000

    Age
    11 to 14
    Challenge level

    Weekly Problem 49 - 2013
    What is the value of 2000 + 1999 × 2000?

  • Small tomato seedlings in pink pots.
    problem

    Reverse Subtraction

    Age
    11 to 14
    Challenge level

    What is the value of c in this subtraction?

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