Geologist: A new method for forecasting earthquakes has reliably predi

Question

Geologist: A new method for forecasting earthquakes has reliably predicted several earthquakes. Unfortunately, this method can predict only that an earthquake will fall somewhere within a range of two and a half points on the Richter scale. Thus, since a difference of two and a half points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage, the new method is unlikely to be useful.

Which one of the following, if assumed, enables the geologist’s conclusion to be properly inferred?

(A) Even if an earthquake-forecasting method makes predictions within a very narrow range on the Richter scale, this method is not likely to be useful unless its predictions are reliable.

(B) An earthquake-forecasting method is unlikely to be useful unless its predictions always differentiate earthquakes that are barely noticeable from ones that result in substantial destruction.

(C) An earthquake-forecasting method has not been shown to be useful until it has been used to reliably predict a large number of earthquakes.

(D) Several well-established methods for forecasting earthquakes can predict within much narrower ranges than two and a half points on the Richter scale.

(E) An earthquake-forecasting technique, even a perfectly reliable one, will probably be of little use if its predictions never distinguish between earthquakes that are imperceptibly small and those that cause catastrophic damage.

ankushsambare · Answer

Conclusion:
The new earthquake forecasting method is unlikely to be useful.
Why?
 
 The method predicts earthquakes only within a wide range: 2.5 Richter points. 
 A 2.5-point difference could mean either a tiny quake or a damaging one. 
 So the geologist thinks the method is not useful.  
To make this conclusion valid, we need an assumption saying:
If a forecasting method cannot distinguish between harmless and dangerous earthquakes, it is probably not useful.
Check choices:
(A) Talks about reliability. The method is already said to be reliable, so irrelevant.
(B) Too strong because it says predictions must “always” differentiate. The conclusion only says “unlikely to be useful,” not impossible to be useful.
(C) Talks about needing many predictions. Irrelevant.
(D) Comparing with other methods does not prove this one is useless.
(E) Correct. It says even a perfectly reliable method will probably be of little use if it cannot distinguish between tiny earthquakes and catastrophic ones. This directly supports the conclusion.
 Answer: (E)

TheYagami · Answer

correct ans should be E 
It says even a perfectly reliable technique is of little use if it cannot distinguish tiny and catastrophic earthquake

guddo · Answer

Geologist: A new method for forecasting earthquakes has reliably predicted several earthquakes. Unfortunately, this method can predict only that an earthquake will fall somewhere within a range of two and a half points on the Richter scale. Thus, since a difference of two and a half points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage, the new method is unlikely to be useful. 
 
Which one of the following, if assumed, enables the geologist’s conclusion to be properly inferred?

The geologist accepts that the method has made reliable predictions, but says it is unlikely to be useful because its predicted range is too wide.  The missing principle  must connect that wide range to usefulness: a useful earthquake forecast must  always distinguish minor earthquakes from seriously damaging ones .

(A) Even if an earthquake-forecasting method makes predictions within a very narrow range on the Richter scale, this method is not likely to be useful unless its predictions are reliable.

Wrong. This says reliability is necessary, but the method already has reliably predicted several earthquakes. It does not explain why the 2.5-point range makes the method unlikely to be useful.

(B) An earthquake-forecasting method is unlikely to be useful unless its predictions always differentiate earthquakes that are barely noticeable from ones that result in substantial destruction.

Correct. The new method gives only a 2.5-point range, and such a range can fail to distinguish between a barely noticeable earthquake and a damaging one. If a method is unlikely to be useful unless it always makes that distinction, then the geologist’s conclusion follows.

(C) An earthquake-forecasting method has not been shown to be useful until it has been used to reliably predict a large number of earthquakes.

Wrong. The issue is not the number of predictions. The geologist’s reasoning is based on the width of the predicted Richter-scale range.

(D) Several well-established methods for forecasting earthquakes can predict within much narrower ranges than two and a half points on the Richter scale.

Wrong. Other methods may be better, but that does not prove this new method is unlikely to be useful.

(E) An earthquake-forecasting technique, even a perfectly reliable one, will probably be of little use if its predictions never distinguish between earthquakes that are imperceptibly small and those that cause catastrophic damage.

Wrong. This is too extreme. The stimulus says the method can fail to distinguish between minor and damaging earthquakes, not that it never makes such distinctions.

Answer: (B)

Geologist: A new method for forecasting earthquakes has reliably predi

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Geologist: A new method for forecasting earthquakes has reliably predi

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

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Perfect 805 Score Debrief by Julia

My Rewards