The negation test works on CR Assumption questions. Assumptions basically complete the argument (i.e. when verbalized, they become premises), and therefore they support the conclusion. On GMAT Assumption questions, it is common for several choices to support the argument, and often these choices all “sound good.” The trick is to sort out the truly necessary statement from the merely helpful statements.
Rather than being a supporting statement, the correct Assumption is a statement that’s opposite (negation) would kill the argument.
For example, here’s one from GMATPrep.
CR_18.JPG [ 101.34 KiB | Viewed 3037 times ]
Notice the “on which the argument depends
” language, not simply “what helps the argument?”
If we mistakenly look for answers that support, we might think the following:
(A) Supports: Large tranquilizer dose. Possible overdose? This does seem to indicate that the tranquilizer is a problem.
(B) Supports: If uncollared females have increasing fertility, then what else would explain the reduced fertility of the tranquilized/collared females? It would have to be the tranquilizer, the only other difference between the two groups.
(C) Supports: Rules out other factors involved in the tranquilizing, and allows us to conclude the reduced fertility is due to a substance in the tranquilizer.
(D) Supports (maybe): At least it suggests that female rhinos are tranquilized more frequently than males, and would be affected more by whatever substance is in the tranquilizer.
(E) Neutral: Just a fact about the tranquilizer.
You can see how unproductive this thought process is! The choices start to sound similar, and you could talk yourself into almost any one.
In contrast, if we negate each statement to see the effect on the conclusion (“some substance in the tranquilizer inhibits fertility”), the correct answer stands out. I’ve put the negated idea/word(s) in caps.
(A) The tranquilizer dose is NOT large. No effect on the conclusion.
(B) The fertility rate of uncollared female rhinos has been STEADY or DECLINING. No effect on the conclusion.
(C) The stress of being tranquilized and handled DOES have a negative effect on fertility. This kills the conclusion that some substance in the tranquilizer is to blame.
(D) Male rhinos lose their collars AS FREQUENTLY as females. No effect on the conclusion.
(E) The tranquilizer used on the rhinos is DIFFERENT than that used on other large mammals. No effect on the conclusion.
The correct answer is C.
Emily Sledge | Manhattan GMAT Instructor | St. Louis
Manhattan GMAT Discount | Manhattan GMAT Course Reviews | Manhattan GMAT Reviews