If the computer in office 4 was bought in 1988, then which one of the following statements must be true?
shaaseJune 23, 2020
Q11 question
In the video, we see that the computer in office 3 was bought in 1988 for this hypothetical; how do we know that the computer in office 2 is 1989 from that? The rules only state that C2 cannot equal C3. Wouldn't this mean that C2 could be either 87/89?
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We can determine that the computer in office 2 was bought in 89 because of the rule that you mention (Rule #4) in addition to Rule #2. Let's walkthrough this.
The question tells us that the computer in office 4 was bought in 1988. Rule #5 tells us that the computer in office 1 and the printer in office 3 were also bought in 1988. This gives us a starting diagram of: C: 88 __ __ 88 P: __ __ 88 __ 1 2 3 4
Rule #1 says that the computer will always be bought in the same year as or an earlier year than the printer in the same office. This means that the printer in office 1 will be either 88 or 89, the computer in office 3 will be either 87 or 88, and the printer in office 4 will be either 88 or 89. C: 88 __ (87/88) 88 P: (88/89) __ 88 (88/89) 1 2 3 4
However, Rule #3 says that the computer in office 3 and the printer in office 4 are from the same year. The only year they have in common as a possibility is 88, which gives us: C: 88 __ 88 88 P: (88/89) __ 88 88 1 2 3 4
Rule #2 says that the printer in office 1 and the computer in office 2 are from the same year. We already know that the printer in office 1 is from either 88 or 89, so that means the computer in office 2 must also either be from 88 or 89. However, Rule #4 says that the computer in office 2 is from a different year than the computer in office 3. We know that the computer in office 3 is from 88, so the computer in office 2 cannot be from 88. This leaves 89 as the only remaining possibility. Therefore, we can assign 89 to both the computer in office 2 and the printer in office 1. This gives us: C: 88 89 88 88 P: 89 __ 88 88 1 2 3 4
Lastly, since Rule #1 says the printer will always be from the same year or a later year than the computer in the same office, we know that the only option for the printer in office 2 is 89 (because the computer was bought in 89 and 89 is our latest option). So, our final diagram is: C: 88 89 88 88 P: 89 89 88 88 1 2 3 4
Therefore, (B) is correct.
Does that make sense? Hope it helps! Please let us know if you have any other questions!
shaaseJune 25, 2020
This is extremely helpful, thank you so much for the in-depth explanation/clarification!
