Combinatorics and Probability

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This chapter contains exercises with a wide range of difficulty, where the emphasis is often on the reasoning, not just the final answer. As both Combinatorics and Probability are among the less intuitive topics, students often struggle with it and need significant support from their teacher to understand and communicate their own thinking. The Solutions/Examples parts in this chapter generally only show one way of approaching the task, please note that at times there are several correct processes. Additional practical information relating to this chapter: 
  • Prism 333, 444 or 555 refers to a prism built from two Logifaces blocks that has a height of 3, 4 or 5 units. 
  • We use the notation Cnk for "n choose k", the number of ways to choose an (unordered) subset of k elements from a fixed set of n elements, so Cnk=n!k!(n-k)!.
  • Probability of an event: 
Pr(event)=number of favourable outcomestotal number of outcomes, where all outcomes are equally likely.
  • By Total number of outcomes we refer to the whole 9 or 16 pcs Logifaces Set, instead of the total 11 different existing Logifaces pieces.
  • The addition rule of probability states for two events A and B that
 P(AB)=P(A)+P(B)-P(AB).
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