The Counting 2 exercise appears under the ***. This exercise used to be on one of the missions under The World of Math, but it was removed due to reordering, renaming, or other changes. This exercise plays with some of the counting techniques.

Types of Problems

There are three types of problems in this exercise:

  1. Combination: This problem has a selection from a group of objects where order is not relevant. The student is asked to fid out how many possibilities there are in the situation.


  2. Multiplication principle: This problem has a situation described where multiple selection are needed. The student is asked to find the number of total possibilities.

    Multiplication principle

  3. Arithmetic sequence: This problem describes a person counting from a certain number by a certain amount. The student is asked to find the number that the counter will stop on.

    Arithmetic sequence


This exercise is easy to get accuracy badges and speed badges because although the numbers change, the problems themselves are very consistent in their difficulty. User just needs to learn how to do the three types.

  1. The Combination problem seems to always be handshakes. If it is, a combination where user chooses two can be performed by taking the given number of people, subtracting one, multiplying those numbers together, and dividing by two.
  2. The multiplication principle means to take the possible outcomes for each part of the event, and multiply those numbers together for the total number of possibilities.
  3. For the Arithmetic sequence problem user can use arithmetic sequences from pre-calculus. In other words, take the first number and add the product of the difference between numbers and one less than the term that they want.

Real-life Applications

  1. Knowing how to count is essential for learning algebra and the higher maths, and counting is used for almost everything humans do.

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