Divisibility

  • Oh! Hidden Inside?
    problem

    Oh! Hidden Inside?

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

    Find the number which has 8 divisors, such that the product of the divisors is 331776.

  • Place value, integers, ordering and rounding - Short Problems
    problem

    AB Search

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

    The five digit number A679B, in base ten, is divisible by 72. What are the values of A and B?

  • Factoring factorials
    problem

    Factoring Factorials

    Age
    11 to 14
    Challenge level
    filled star filled star filled star

    Find the highest power of 11 that will divide into 1000! exactly.

  • Adding in Rows
    problem

    Adding in Rows

    Age
    11 to 14
    Challenge level
    filled star filled star filled star

    List any 3 numbers. It is always possible to find a subset of adjacent numbers that add up to a multiple of 3. Can you explain why and prove it?

  • Powerful factorial
    problem

    Powerful Factorial

    Age
    11 to 14
    Challenge level
    filled star filled star filled star

    6! = 6 × 5 × 4 × 3 × 2 × 1. The highest power of 2 that divides exactly into 6! is 4 since (6!) / (2^4) = 45. What is the highest power of two that divides exactly into 100!?

  • Missing Digit
    problem

    Missing Digit

    Age
    11 to 14
    Challenge level
    filled star filled star filled star

    What digit must replace the star to make the number a multiple of 11?

  • Plastic human skeleton on a blue background.
    problem

    Skeleton

    Age
    11 to 14
    Challenge level
    filled star filled star filled star

    Can you reconstruct the long division calculation from the 'skeleton'?

  • N000ughty thoughts
    problem

    N000ughty

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

    How many noughts are at the end of these giant numbers?

  • Mod 3
    problem

    Mod 3

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

    Prove that if a^2+b^2 is a multiple of 3 then both a and b are multiples of 3.

  • 396
    problem

    396

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

    The four digits 5, 6, 7 and 8 are put at random in the spaces of the number : 3 _ 1 _ 4 _ 0 _ 9 2 Calculate the probability that the answer will be a multiple of 396.