55.1.4 Among the various models

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How is A a sufficient assumption? I didn't like any of the answer choices, so I pretty much guessed on this one. I thought A was the least attractive answer choice because it lacks the conditional nature that is typical for sufficient assumptions. My understanding of the argument is this:

We can't figure out how effective a certain model cleans simply be looking at how powerful the motor is. This is because the efficiency varies a lot, even with identical motors.

The sufficient assumption I was looking for was this: if efficiency varies (even with identical motor power), then we can't determine how effective the model cleans.

How does A paraphrase this?

c.janson35

There are times when a sufficient assumption does not take the form of a conditional--this is one of those cases.

The conclusion is we cannot measure effectiveness by knowing power. Why? Because even when power is identical, the efficiency varies.

Ok, but why does efficiency matter for effectiveness? This is what we need, something that connects the two ideas.

If it is true that the efficiency has a significant impact on effectiveness, as A says, then we can properly draw the conclusion: we won't be able to tell effectiveness solely by motor power because two identical powers may have widely varying efficiencies, and efficiencies have a huge impact on effectiveness.

Hope this helps!

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@c.janson35 Thanks!

But doesn't this seem more like a necessary assumption rather than a sufficient assumption? After reading your explanation, I do see why A is the best answer choice (since it links up efficiency and effectiveness), but I don't think it really is a sufficient assumption. In order for it to be sufficient, don't you need to assume that the higher the efficiency, the higher the effectiveness? Efficiency and effectiveness are two completely different ideas, A only tells us that they are related, but not the direction of how they are related. You can have things be very efficient, but not be effective at all (and vice versa).

c.janson35

You don't need to assume the higher the efficiency the higher the effectiveness because the conclusion is only limited to whether or not you can ascertain the effectiveness of a particular model from knowledge about motor power alone. Our task if very direct and specific for SA questions, and that is only to prove the conclusion is 100% true. A fulfills this requirement for us, because we cannot know the effectiveness of a motor by its power alone, because identical powers may have different efficiencies, and if efficiencies are a determining factor to effectiveness, then it is 100% true that only knowing motor power cannot provide us with information about effectiveness.

We don't care if higher efficiency means more effectiveness, only that they are related. How they are related is immaterial to the conclusion.