Unplugged Practice Test: Logical Reasoning Set 1, Question 10 (Necessary Assumption)
Taking the test? Finish it first. This page shows the answer.
- Necessary Assumption questions ask for the unstated premise the argument depends on.
- Try the negation test. If negating a choice wrecks the argument, that choice is the necessary assumption.
- Every question on this test is original, written to the same logical skeletons as real questions, and Steve checked every one himself before release.
The question
A roadside message sign, like a radio traffic bulletin, gives drivers information they could not gather from the road ahead of them, and each one lets a transit agency warn of a hazard and explain what is causing a delay. Yet the text posted on a message sign is on occasion at odds with the conditions drivers actually meet. A message sign is therefore not the equivalent of a radio traffic bulletin.
10. Which one of the following is an assumption on which the argument depends?
- (A)A radio traffic bulletin is never meant to deceive the drivers who hear it.
- (B)The content of a radio traffic bulletin is never at odds with the conditions drivers actually meet.
- (C)Information that drivers need in order to choose a route is sometimes supplied only by message signs.
- (D)Transit agencies sometimes post text they know to be inaccurate in order to divert traffic.
- (E)On routes equipped with message signs, radio traffic bulletins are sometimes still necessary.
BWhy (B) is correct
(B) is what the argument needs. The stimulus says a message sign differs from a radio bulletin because a sign's text is sometimes at odds with what drivers actually meet on the road. That gap only marks a real difference between the two if a radio bulletin never has that same problem, so the argument depends on radio bulletins always matching the conditions drivers meet.
Why the other answers are wrong
AWhy (A) is wrong
(A) that a radio bulletin is never meant to deceive drivers is stronger than needed and off point, since being at odds with conditions doesn't require any intent to mislead.
CWhy (C) is wrong
(C) says the information drivers need in order to choose a route is sometimes supplied only by message signs, which addresses usefulness, not whether the sign's text ever conflicts with conditions.
DWhy (D) is wrong
(D) points at transit agencies sometimes posting text they know is false. That speaks to motive, which the argument never needs to establish.
EWhy (E) is wrong
(E) that radio bulletins are sometimes still necessary on routes with message signs doesn't touch whether either source's content ever clashes with conditions on the road.
Common questions
What type of question is this?
Necessary Assumption. Necessary Assumption questions ask for the unstated premise the argument depends on.
How do I get better at Necessary Assumption questions?
Try the negation test. If negating a choice wrecks the argument, that choice is the necessary assumption. The free LSAT cheat sheet lists the wrong-answer patterns to watch for on every type.
