Unit 12 · Multi-Step Conditional Reasoning

Observatory Excursion — Are Both Reasoners Correct?

Lesson 11 of 16

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A class rule: the only children NOT going to the observatory are those playing in the soccer match. Maliyan says: Mei doesn't play soccer, so she must be going. Robyn says: Kirra isn't going, so she must be playing soccer. Both sound sensible — and for once, both ARE correct. This question is the positive counterpart to the 'necessary vs sufficient' confusion questions: sometimes BOTH people get the logic right, and the answer really is 'both'.

Chapters

0:00Introduction
0:22The Question
1:05Strategy
1:39Step 1: Decode the biconditional rule
2:16Step 2: Check Maliyan's reasoning
2:42Step 3: Check Robyn's reasoning and conclude
3:27Correct answer

Question

Mei and Kirra's class is due to go on an excursion to an observatory so they can look at the stars through the big telescope. The only children in the class who are not going on the excursion are the ones who need to play in the soccer match.

Maliyan: "Mei does not play soccer, so she must be going to the observatory."

Robyn: "Kirra is not going to the observatory, so she must be playing in the soccer match."

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

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Observatory Excursion — Are Both Reasoners Correct? | Multi-Step Conditional Reasoning | GoTestPrep