LSAT Explanation PT 27, S4, Q9: The only physical factor preventing a

LSAT Question Stem

Which one of the following is an assumption on which the argument depends? 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is E. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The passage states that the only physical factor preventing a human journey to Mars has been weight, specifically the weight of carrying enough fuel for the round trip. The passage then introduces a device that can manufacture fuel from the Martian atmosphere for the return trip, thus making a human journey to Mars possible. The structure of the argument is as follows:

Premise: Weight of carrying enough fuel for a round trip to Mars has been the only physical factor preventing human journey to Mars.

Premise: A device has been invented that can manufacture fuel from the Martian atmosphere for the return trip.

Conclusion: It is possible for people to go to Mars in a spacecraft that carries this device and then return.

The question type for this problem is Necessary Assumption, which means we need to identify an assumption that must be true for the argument to hold.

Let's evaluate each answer choice:

a) While it would be convenient if the amount of fuel needed for the return trip was the same as the amount needed for the trip to Mars, it's not necessary for the argument to hold. The device could still make the journey possible even if the fuel amounts were different.

b) The composition of the fuel is not a necessary assumption for the argument. As long as the device can produce fuel that can power the spacecraft for the return trip, the specific composition of the fuel is not crucial.

c) The device taking up some of the crew's living space may be inconvenient, but it doesn't necessarily prevent the journey from being possible. The argument can still hold even if the device takes up some living space.

d) The cost of constructing the spacecraft with the device is not a necessary assumption for the argument. The argument is focused on the weight and feasibility of the journey, not the cost.

e) This is the correct answer. The argument assumes that the device for manufacturing fuel weighs less than the tanks of fuel that a conventional spacecraft would need to carry from Earth for the return trip. If the device weighed the same or more than the fuel tanks, it would not solve the weight issue, and the argument would not hold.

An "Evaluate" question for this argument could be: "Does the device for manufacturing fuel from the Martian atmosphere weigh less than the fuel tanks needed for the return trip?"

In conclusion, the necessary assumption for the argument is that the device for manufacturing fuel for the return to Earth weighs less than the tanks of fuel that a conventional spacecraft would otherwise need to carry from Earth for the return trip (answer choice E).