PT23.S2.Q10

PrepTest 23 - Section 2 - Question 10

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All bridges built from 1950 to 1960 are in serious need of rehabilitation. ████ ███████ ███████████ ██ ████ ███████ ████████ ████ █████ █████████ ██ ██████ ███████████ ███████ ████ ██ ███ ███ █████ ███ ████ ████ ██ ████ ██ █████ ████ ███████ ██ ███████ ████ ██ ██████████████ ███ ███ ██████████ ████████ █████ ██ ██████████ ███████ ███ █████ ███ ███████ ████ ████ █████ █████████ ██ ██████ ███████████ ███████

The Stimulus’ Claims Distilled

In Must Be True questions, we can just treat the stimulus as a big ol’ list of rules – 10 commandments style – any one of which could hold the key to the correct answer. Here are formal logic translations of the claims, with links to their English anchor points in the stimulus:

  1. 50s → Rehab
  2. 50s ←some→ Faulty
  3. Rehab ←some→ /Suspension
  4. Faulty → /Suspension

If you’re super-dee-duperly attuned to the valid argument forms, you might proactively anticipate two “some before all” inferences that can be drawn from these claims:

  1. Some faulty bridges need rehab. (Faulty ←some→ 50s → Rehab)
  2. Some 50s bridges aren’t suspension. (50s ←some→ Faulty → /Suspension)

Figuring those out in advance is nice if you’re locked in and you can work them out quickly and with high confidence. Relying on process of elimination is totally fine, though. I personally tend to anticipate and diagram a lot and even I relied on PoE here.

Show answer
10.

If the statements above are █████ █████ ██ ███ █████ ██ █████ ███████████ █████ ███ ██ ███ █████████ ████ ████ ██ █████

a

Some suspension bridges ███ ███ ██ ███████ ████ ██ ███████████████

The stimulus tells us some bridges that do need rehab aren’t suspension bridges, so (A) attempts to take the contrapositive of that “some” claim, which isn’t allowed.

Working from a different angle, the stimulus tells us all suspension bridges are not-faulty, but none of the stimulus’ claims take us from “not faulty” to [anything]. In other words, “not faulty” never appears in a claim’s sufficient condition, so it’s a dead end as we try to build a conditional chain from suspension to not-rehab.

b

Some suspension bridges ███ ██ ███████ ████ ██ ███████████████

The stimulus tells us some bridges that need rehab aren’t suspension bridges, but that doesn’t mean other bridges that need rehab are suspension bridges – “some” can include “all.” That is, the claim above leaves room for all rehab bridges to be non-suspension bridges.

Working from a different angle, the stimulus tells us all suspension bridges are not-faulty, but none of the stimulus’ claims take us from “not faulty” to [anything]. In other words, “not faulty” never appears in a claim’s sufficient condition, so it’s a dead end as we try to build a conditional chain from suspension to rehab.

c

Some bridges that ████ █████ █████████ ██ ██████ ███████████ ██████ ███ ██ ███████ ████ ██ ███████████████

This puts a “some” claim before an “all” claim, which is a valid argument form:

English
Some faulty bridges were built in the 50s.*
All bridges built in the 50s need rehab.
________
Some faulty bridges need rehab.
Logic
Faulty ←some→ 50s*
50s → Rehab
________
Faulty ←some→ Rehab

*“Some” claims are reversible.

d

Some bridges built ████ ████ ██ ████ ███ ███ ██ ███████ ████ ██ ███████████████

This must be false. The stimulus’ first sentence tells us all 50s bridges need rehab.

e

Some bridges that ████ █████ █████████ ██ ██████ ███████████ ██████ ███ ███ ███████ █████ ████ ██████████ ████████

The double-negative is annoying – (E) just says “Some faulty bridges are suspension bridges.”

This must be false. The stimulus’ last sentence tells us no suspension bridges are faulty.

Confirm action

Are you sure?