Quarter Wit, Quarter Wisdom: An Official Assumption Question

Quarter Wit, Quarter WisdomToday we will look at an OG question of critical reasoning (as promised last week). We will use the concept discussed last week – remember what an assumption is. An assumption is a missing necessary premise. It will bring in new information essential to the conclusion.

Now let’s jump on to the OG question.

Question: A recent report determined that although only three percent of drivers on Maryland highways equipped their vehicles with radar detectors, thirty-three percent of all vehicles ticketed for exceeding the speed limit were equipped with them. Clearly, drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are drivers who do not.

The conclusion drawn above depends on which of the following assumptions?

(A) Drivers who equip their vehicles with radar detectors are less likely to be ticketed for exceeding the speed limit than are drivers who do not.

(B) Drivers who are ticketed for exceeding the speed limit are more likely to exceed the speed limit regularly than are drivers who are not ticketed.

(C) The number of vehicles that were ticketed for exceeding the speed limit was greater than the number of vehicles that were equipped with radar detectors.

(D) Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.

(E) Drivers on Maryland highways exceeded the speed limit more often than did drivers on other state highways not covered in the report.

Solution:

Let’s look at the question stem first. We need to find an assumption. An assumption is a missing necessary premise. Something that will not only strengthen the conclusion but also be essential to the argument.
An assumption is a statement that needs to be added to the premises for the conclusion to be true. Let’s first find the premises and the conclusion of this argument.

Premises:

- Only 3% of drivers on Maryland highways had radar detectors.

- 33% of vehicles that got speeding tickets had radar detectors.

Conclusion:

Drivers with radar detectors are more likely to exceed the speed limit regularly than other drivers.

There must be some disconnect between the premises and conclusion since there is an assumption in the argument. Look carefully. Premises give you the connection between ‘vehicles that have radar detectors’ and ‘vehicles that get speeding tickets’. The conclusion, on the other hand, concludes a relation between ‘vehicles that have radar detectors’ and ‘vehicles that exceed the speed limit’. The assumption must then give a connection between ‘vehicles that get speeding tickets’ and ‘vehicles that exceed speed limit’.

To clarify it further,

A – vehicles that have radar detectors

B – vehicles that get speeding tickets/vehicles that were ticketed for speeding

C – vehicles that exceed the speed limit

Premises:

- Only 3% of all vehicles are A

- 33% of B are A

Conclusion:

- A are  more likely to be C

The assumption needs to be something that links B to C i.e. that links ‘vehicles that get speeding tickets’

to ‘vehicles that exceed the speed limit’. Option (B) gives us that relation. It says ‘B are more likely to be C’.

Lets add it to premises and see if the conclusion makes more sense now:

- Only 3% of drivers on Maryland highways had radar detectors.

- 33% of vehicles that got speeding tickets had radar detectors.

- Drivers who get speeding tickets are more likely to exceed the speed limit regularly than others.

Conclusion: Drivers with radar detectors are more likely to exceed the speed limit regularly than other drivers.

Now it makes sense!

Let’s take a quick look at the other options and see why they don’t work. We will retain the A, B, C structure given above.

Option (A) says ‘A are less likely to be B’ – Cannot be our assumption

Option (C) only tells us that number of B are greater than number of A.

Option (D) tells us that many vehicles were ticketed multiple times.

Option (E) compares drivers on Maryland highways with drivers on other state highways. This is out of scope.

It is clear that option (B) is the outright winner. This question is one of the tougher questions. You can easily handle it using this technique. We hope you will be able to put this technique to good use.

Karishma, a Computer Engineer with a keen interest in alternative Mathematical approaches, has mentored students in the continents of Asia, Europe and North America. She teaches the GMAT for Veritas Prep and regularly participates in content development projects such as this blog!

2 Responses

  1. carcass says:

    great question and explanation :)

  2. jaseem says:

    Hi , C should be “vehicles that exceed the speed limit regularly”. The world “vehicles that exceed the speed limit regularly” has to be connected to B .

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