Self-study
Support Whoever murdered Jansen was undoubtedly in Jansen's office on the day of the murder, and Support both Samantha and Herbert were in Jansen's office on that day. ██ ███████ ███ █████████ ███ ███████ ███ ██████ █████ ████ █████ ██████ ███ ████████████ ██ ███ ██████████ ██ ███ █████ ██ ███ ██████ ███ ██ ████████ ███ ███ █████████ ███ █████ ████ ███████ ███████ ██████ ██████████ ██ █████████████ ███ ██████ █████ ████████████ ███ ██ ██████████ ██ ███ █████ ██ ███ ██████ █████ ███ ████████████ ████ ███ ██████████ ██ ██ ███ ███ █████████ ████ ████████ ████ ██ ███ ███████
Summary
The author accuses Samantha of murdering Jansen, and the support list is long:
Samantha and Herbert fulfill a requirement of the murderer (in office on that day).
If Samantha is the murderer, the police won’t find her fingerprints or footprints; the police didn’t find her footprints, and we don’t know if they found her fingerprints.
If Herbert is the murderer, the police would’ve found either Herbert’s fingerprints or footprints, but they found neither. From this the author draws a valid sub-conclusion that Herbert is not the murderer.
Using this sub-conclusion, the author concludes that Samantha must be the murderer.
Missing Connection
Herbert’s innocence has been proven, but why is Samantha the only other option? Other people could have been in the office that day. We can’t assume that just because Herbert isn’t guilty, that Samantha is. To do that, we need to know that these are the only two options.
20.
Which one of the following, ██ ████████ ██████ ███ ██████████ ████ ████████ ███ ███ ██████ ██ ██ ████████ █████████
a
If there had ████ ██████████ ██ ███ █████ ██ ███ ██████ ███ ██████ █████ ████ █████ █████
We were already given conditional rules for Samantha and Herbert’s footprints about what police would or wouldn’t find, and we were given results to compare to those rules. This doesn’t help us conclude that Samantha is the murderer.
b
Jansen's office was ███ █████ ██ ███ ██████
Irrelevant. The scene of the crime could have been anywhere.
c
No one but ███████ ███ ████████ ███ ██ ████████ ██████ ██ ███ ███ ██ ███ ███████
If this is true, we only have two options to choose from and Herbert has been proven innocent. We can validly conclude that Samantha is the murderer.
d
The fingerprints found ██ ███ █████ ██ ███ █████ ████ ███ █████████
We still don’t know who the fingerprints belong to. Also, even if we know that they aren’t Samantha’s, that only fulfills a necessary condition of Samantha as murderer. It doesn’t solve the larger problem: Why couldn’t the murderer be someone other than Herbert or Samantha?
e
The fingerprints found ██ ███ █████ ██ ███ █████ ████ ███ ███████████
Related to the explanation of (D): This only fulfills a necessary requirement of Samantha being the murderer. It’s possible that the fingerprints don’t belong to Samantha, but someone other than Samantha or Herbert killed Jansen.