Combinatorics (Primary)

Theory

What is combinatorics?

Combinatorics is the branch of mathematics that deals with counting — not just by listing, but by using smart rules and patterns to calculate the number of ways something can happen.

We’ll explore questions like:

  • How many different outcomes are possible when making choices?
  • What’s the difference between arrangements (where order matters) and selections (where it doesn’t)?
  • How can we use multiplication, permutations, and combinations to solve these problems?

Problems

  1. A toy shop sells 5 types of teddy bears and 3 types of toy cars. How many different teddy-and-car combinations can you choose?

  2. A toy shop sells 5 types of teddy bears, 3 types of toy cars, and 4 types of spinning tops. How many different choices are there if you pick:
    a) one teddy bear, one toy car, and one spinning top?
    b) any two different toys?

  3. How many four-digit numbers are there such that:
    a) only even digits are used?
    b) there is at least one even digit?
    (Hint: Even digits are 0, 2, 4, 6, 8.)

  4. You flip a coin three times. How many different possible outcomes (sequences of heads and tails) are there?

  5. Each square in a 2×2 grid is coloured either black or white. How many different ways are there to colour the grid?

  6. In the fictional Mumbo-Yumbo language, the alphabet has just two letters: A and U. A “word” can be any sequence of up to 5 letters. How many different words are there in the Mumbo-Yumbo dictionary?

  7. A football team has 11 players. In how many ways can you choose:
    a) a captain and a vice-captain (two different people)?
    b) two strikers (order doesn’t matter)?

  8. How many ways can you place:
    a) a black rook and a white rook on a chessboard?
    b) a black king and a white king, such that they don’t attack each other?
    (Reminder: Rooks attack any square in the same row or column. Kings attack all adjacent squares.)

  9. Charlie has 4 different-coloured counters. In how many different ways can he arrange them in a row?

  10. How many five-digit numbers can be formed using only odd digits, such that each digit is different?
    (Hint: Odd digits are 1, 3, 5, 7, 9.)

  11. Which are more numerous: seven-digit numbers that include the digit 1, or those that don’t contain the digit 1 at all?

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Our courses

Where do you hold your classes?
We hold our classes online or on-site on Saturdays at our branch in Pimlico Academy, London.
You can find our timetable here.
What do you need to start learning online?
For lessons you only need a computer or phone with a microphone, camera and Internet access. Wherever you are - in London, Nottingham, New York or Bali - online lessons will be at hand.
When can I take the trial lesson?
You can get acquainted with the school at any time convenient for you. To do this, just leave a request and sign up for a lesson.
What should I expect from the trial lesson?
The trial lesson is a 30-minute online session designed to get a sense of how your child approaches mathematical thinking and problem solving. (In practice, it often runs a bit longer if the student is engaged!)

We typically explore a range of fun and challenging problems drawn from competitions. We adapt the difficulty based on how the student responds, aiming to make it both accessible and stimulating.

After the session, we’ll have a quick conversation with the parent to share observations and suggest a personalised path forward.
I can't attend class, what should I do?
It is OK, it happens! Students have the opportunity to cancel a lesson up to 8 hours before the scheduled time without loss of payment. So you can reschedule it for a convenient time, and the teacher will have the opportunity to
I don't have much free time, will I have time to study?
Learning can take place at your own pace. We will select a convenient schedule and at any time we will help you change the schedule, take a break or adjust the program.
How long is one lesson?
All classes last 1 hour.
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