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Given info: must/cannot be true/false | Quick guide

"Must be true" questions

Must be true means that the answer is a statement that is always true, in any circumstance that is acceptable to the rules.
The wrong choices to a “must be true” question are choices that could or must be false. They don’t have to be true, because you can find at least one viable scenario in which that statement isn’t true.

"Must be false" questions

Must be false means that the answer is a statement that is always false—or impossible—in any circumstance that is acceptable to the rules. In other words, the answer breaks at least one of the rules when you implement the statement.
The wrong choices to a “must be false” question are choices that could or must be true. They can be possible in at least one scenario.
Top tip: It can be helpful to think of must be false as “impossible”, and both could be true and could be false as “possible.”

Checklist

Since you aren’t given new information here, the answer is obtainable from your initial diagram and rules.
✓ Check your diagram and deductions
It’s possible that the answer is immediately evident from the deductions you’ve already made. If it’s not immediately evident, eliminate any choices that are obviously wrong from your diagram and rules.
✓ Test whatever choices remain
It can be a little tricky to remember how to test choices for must questions.
  • "Must be true" questions — Test the choices by trying to make the choices false. If you make the statement in the choice false, and you can still make an acceptable scenario, eliminate that answer!
  • "Must be false" questions — Test the choices by trying to make the choices possible. If you can incorporate the info in the choice into your diagram and generate an acceptable scenario, then eliminate that choice!
Top tip: If only two choices remain, and you feel confident in your work so far, you can just test one of them—if it accomplishes what you need (whether it’s a must be true or must be false) then it’s the answer! If it doesn’t accomplish what you need, then the other remaining choice is the answer.

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