Unit 12 · Multi-Step Conditional Reasoning

Fire Alarm — What Can We Conclude?

Lesson 4 of 16

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About this lesson

Two people look at the same information and each draw a different conclusion. Your job is to decide which of them — if either — is reasoning correctly. This question introduces one of the most important logical ideas in OC TS: the difference between what an alarm going off TELLS you and what an alarm staying SILENT tells you. These are two very different things.

Chapters

0:00Introduction
0:23The Question
1:09Strategy
1:51Step 1: Check Yuri — morning alarm can't be a drill
2:38Step 2: Check Bindi — silence doesn't rule out fire
3:36Correct answer

Question

When the fire alarm goes off, it could either be a real fire, or it could be a fire drill. Fire drills can be scheduled for any day of the week, but they always happen at exactly 2 o’clock in the afternoon.

Yuri says: “If the fire alarm goes off during the morning, you know it must be a real fire!”

Bindi says: “Even if the fire alarm is not going off, it doesn’t mean that there isn’t a fire.”

If the information in the box is true, whose reasoning is correct?

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