No need to try every case: push to the extreme and the answer shows itself.
- 1Maximum and Minimum Problems9:15
- Now playing: 2Worst-Case Thinking4:24
- 3The Pigeonhole Principle6:58
Know Without Trying: Worst-Case Thinking
Methods in this video
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- 1
Everything else first, plus one
When to use it: The question says to be certain, to be sure, ensure or make sure, and asks how many you must take to be sure of getting a particular one, one of every kind, a third colour or number, or two different ones; or it gives the total and asks which statement must be true (at least how many must be of one kind).
- To be certain means it must work on your unluckiest day, not your luckiest.
- Sort by what you want. Take everything that isn't it, then add one.
- To get every kind: leave out the smallest kind and take everything else.
- Asked the other way: find the most the others can be, then take that from the total.
Practise exam-style questions with these methods
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