Mixed IB recognition practice
Practice Flashcards
Flip to reveal answersFirst question to ask on any counting problem?
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All 8 Flashcards — Mixed IB recognition practice
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Question
First question to ask on any counting problem?
Answer
Does order matter? Arrange/rank/roles → yes (ⁿPᵣ); choose/team/committee → no (ⁿCᵣ). Then check for restrictions.
Question
Trigger: 'together' / 'next to each other'?
Answer
Block method — glue them into one item, arrange, then multiply by the internal orders (k!).
Question
Trigger: 'not together' / 'not adjacent'?
Answer
Total − together (for a pair), or the gap method (seat the others, drop the rest into separate gaps).
Question
Trigger: 'must include' / 'always chosen'?
Answer
Fix that member in place, then choose the rest from those remaining.
Question
Trigger: 'at least' / 'at most'?
Answer
Add up the allowed cases, or use total − unwanted (the complement).
Question
Trigger: repeated letters?
Answer
Divide n! by the factorial of each repeated letter: n! ÷ (p! q! …).
Question
Trigger: 'shortest route on a grid'?
Answer
Choose which of the moves go 'up' (or right): ⁿCᵣ.
Question
Same numbers, different answer — why?
Answer
Because the wording sets the type. Medals (distinct roles) → ⁿPᵣ; a committee (no roles) → ⁿCᵣ.
Read the notes
Full study notes for Mixed IB recognition practice
Topic 1.10 hub
Counting & binomial (HL only)
More from Topic 1.10
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Math AA exam skills
Paper structures & tips
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