If Rivera interviews Ikaba, which one of the following must be true?

GabiKolb on November 19, 2019


Please explain how to find the answer to this

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Irina on November 19, 2019


Sure, let's look at the rules.
This is a hybrid game that requires us to match witnesses to prosecutors and determine the order of interviews over exactly four days. We have four witnesses - F G H I, each interviewed by one of three investigators - Q R S. Each investigator interviews at least one witness and each witness is interviewed by exactly one investigator. This tells us that 3 investigators interview 1 witness and 2 investigator interviews 2 - 2-1-1.

W: __ __ __ __
I: __ __ __ __
1 2 3 4

The interview is governed by the following rules:
(1) G and H must be interviewed by the same investigator.
This rule tells us that whoever interviews G & H is the only investigator that interviews two witnesses, the rest of them interview one witness each - F and I.

(3) G and I cannot be interviewed on consecutive days.

(4) Q must interview F.
Q =F
This rule allows us to infer that either R or S must interview G & H.

(5) R must conduct the third interview.

W: __ __ __ __
I: __ __ R __
1 2 3 4

The question asks us if R interviews I, which of the following must be true?

Let's put this condition on our diagram:

W: __ __ I __
I: __ __ R __
1 2 3 4

Since G and I cannot be interviewed on consecutive days per rule (3), we know that G must be interviewed on day 1.

W: G __ I __
I: __ __ R __
1 2 3 4

We can thus conclude that (B) must be true.

Let's briefly look at the rest of the answer choices. We can eliminate (A) and (E) because G must be first and I must be third. We can eliminate (C) and (D) because H could be either second or fourth, thus it is not true that it must always be second or always be fourth in every scenario as the correct answer to a must be true question requires.

W: G H I F
I: S S R Q
1 2 3 4

W: G F I H
I: S Q R S
1 2 3 4

Let me know if this makes sense and if you have any other questions.