If the fire alarm sounds, the main doors lock automatically. The main doors did not lock this morning. Which conclusion must be true?
Answer and explanation
Correct answer: A. The fire alarm did not sound.
- Step 1: If the alarm always locks the doors, then an alarm and unlocked doors cannot happen together. Step 2. The doors did not lock, so the alarm did not sound. Answer: The fire alarm did not sound. Why not the others: The alarm sounded but the doors were broken.: This goes beyond the statements, which say nothing about broken doors. The doors lock only when the alarm is silent.: This reverses the rule. The alarm sounded later in the day.: This is not supported by the statements.
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