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

First on November 19, 2019


Please explain how to find the answer to this


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.