Critical Reasoning Weakening passages - Five good reasons which can weaken a conclusion
What can indeed weaken an argument or the conclusion? We do not doubt the veracity of the conclusion nor the premises per se. However if a conclusion is drawn after taking into account of a hidden assumption, then we have to be cautious. The assumption itself might lead to wrong conclusion or weaken it. The essential question to first ask is what factor can be there in addition, so that you can not arrive at the given solution. Form an answer of your own and then eliminate all those irrelevant answer choices that are off-scope. In many cases, one or two of the answer choices will strengthen the argument and you can eliminate them first. Pick from the remainder of the choices, one that comes close to your own assumption.
Normally weakeners are:
1. Where a cause is assumed to lead to a conclusion but does not in fact. The average life expectancy for the United States population as a whole is 73.9 years, but children born in Hawaii will live an average of 77 years, and those born in Louisiana, 71.7 years. If a newlywed couple from Louisiana were to begin their family in Hawaii, therefore, their children would be expected to live longer than would be the case if the family remained in Louisiana.
Which of the following, if true, would most seriously weaken the conclusion drawn in the passage?
A. Insurance company statisticians do not believe that moving to Hawaii will significantly lengthen the average Louisianan’s life.
B. The governor of Louisiana has falsely alleged that statistics for his state are inaccurate.
C. The longevity ascribed to Hawaii’s current population is attributable mostly to genetically determined factors.
D. Thirty percent of all Louisianans can expect to live longer than 77 years.
E. Most of the Hawaiian Islands have levels of air pollution well below the national average for the United StatesConclusion:
therefore, their children would be expected to live longer than would be the case if the family remained in Louisiana Weakener:
Their children would not be expected to live longer because…..Reasoning:
People expect the longevity to be higher just because of living in Hawaii. But this is wrong. C provides a factor that says that the longevity is caused in fact by genetics. Hence Choice C weakens the conclusion . Opponents of laws that require automobile drivers and passengers to wear seat belts argue that in a free society people have the right to take risks as long as the people do not harm other as a result of taking the risks. As a result, they conclude that it should be each person’s decision whether or not to wear a seat belt.
Which of the following, if true, most seriously weakens the conclusion drawn above?
A. Many new cars are built with seat belts that automatically fasten when someone sits in the front seat.
B. Automobile insurance rates for all automobile owners are higher because of the need to pay for the increased injuries or deaths of people not wearing seat belts.
C. Passengers in airplanes are required to wear seat belts during takeoffs and landings.
D. The rate of automobile fatalities in states that do not have mandatory seat belt laws is greater than the rate of fatalities in states that do have such laws.
E. In automobile accidents, a greater number of passengers who do not wear seat belts are injured than are passengers who do wear seat belts.Reasoning:
The opponents of the law tend to think that their action does not affect others. But choice B brings out the fact, that other people are also affected because when occupants do not wear their seat belts, and when ther are grievously injured, they have to be paid increased compensations and medical reimbursements by the Insurance companies, which in turn have to hike the insurance premiums, thus affecting others, who are regular belt users. B weakens the conclusion.
2. We assume just one single factor for the effect to be caused, while there may be other factors that may lead to the result Red blood cells in which the malarial-fever parasite resides are eliminated from a person’s body after 120 days. Because the parasite cannot travel to a new generation of red blood cells, any fever that develops in a person more than 120 days after that person has moved to a malaria-free region is not due to the malarial parasite.
Which is the following, if true, most seriously weakens the conclusion above?
A. The fever caused by the malarial parasite may resemble the fever caused by flu viruses.
B. The anopheles mosquito, which is the principal insect carrier of the malarial parasite, has been eradicated in many parts of the world.
C. Many malarial symptoms other than the fever, which can be suppressed with anti-malarial medication, can reappear within 120 days after the medication is discontinued.
D. In some cases, the parasite that causes malarial fever travels to cells of the spleen, which are less frequently eliminated from a person’s body than are red blood cells.
E. In any region infested with malaria-carrying mosquitoes, there are individuals who appear to be immune to malariaReasoning:
We relied upon one fact that any fever that develops in a person more than 120 days after that person has moved to a malaria-free region, could not be due to malaria, since the parasites are eliminated from the blood in 120 days. However, we have failed to notice that there are other alternate places where the parasite resides such as the spleen for more than 120 days Hence D weakens the conclusion.
3. The things that are compared may not be equal.The imposition of quotas limiting imported steel will not help the big American steel mills. In fact, the quotas will help “mini-mills” flourish in the United States. Those small domestic mills will take more business from the big Americal steel mills than would have been taken by the foreign steel mills in the absence of quotas.
Which of the following, if true, would cast the most serious doubt on the claim made in the last sentence above?
(A) Quality rather than price is a major factor in determining the type of steel to be used for a particular application.
(B) Foreign steel mills have long produced grades of steel comparable in quality to the steel produced by the big American mills.
(C) American quotas on imported goods have often induced other countries to impose similar quotas on American goods.
(D) Domestic “mini-mills” consistently produce better grades of steel than do the big American mills.
(E) Domestic “mini-mills” produce low-volume, specialized types of steels that are not produced by the big American steel mills.Reasoning:
The conclusion: Those small domestic mills will take more business from the big American steel mills than would have been taken by the foreign steel mills in the absence of quotas.
We have to say that small domestic mills will not take more business from the big American steel mills
Here we are equating American big mills with American mini-mills. This is wrong. Both are different units in that both have differing product mixes.
The conclusion is derived from faulty, or unrepresentative, or insufficient data. E brings out this fact and thus weakens the conclusion In the United States in 1986, the average rate of violent crime in states with strict gun-control laws was 645 crimes per 100,000 persons—about 50 percent higher than the average rate in the eleven states where strict gun-control laws have never been passed. Thus one way to reduce violent crime is to repeal strict gun control laws.
Which of the following, if true, would most weaken the argument above?
(A) The annual rate of violent crime in states with strict gun-control laws has decreased since the passage of those laws.
(B) In states with strict gun-control laws, few individuals are prosecuted for violating such laws.
(C) In states without strict gun-control laws, many individuals have had no formal training in the use of firearms.
(D) The annual rate of nonviolent crime is lower in states with strict gun-control laws than in states without such laws.
(E) Less than half of the individuals who reside in states without strict gun-control laws own a gun.Reasoning:
Here we are comparing between two types of states based on the face value of the absolute figures. This is wrong. In fact, Choice A brings out the fact that both the types of states are not equal. The states where the law has been brought in had a comparatively higher criminal record than those without such laws. Choice A says that after the law was brought in the crimes came down thus choice A weakens the conclusion that one way to reduce violent crime is to do away with strict gun control laws.
4. Short-term reasons vs long- term reasons
Treatment for hypertension forestalls certain medical expenses by preventing strokes and heart disease. Yet any money so saved amounts to only one-fourth of the expenditures required to treat the hypertensive population. Therefore, there is no economic justification for preventive treatment for hypertension.
Which of the following, if true, is most damaging to the conclusion above?
(A) The many fatal strokes and heart attacks resulting from untreated hypertension cause insignificant medical expenditures but not treating the disease at the right time leads to large economic losses,
(B) The cost, per patient, of preventive treatment for hypertension would remain constant even if such treatment were instituted on a large scale.
(C) In matters of health care, economic considerations should ideally not be dominant.
(D) Effective prevention presupposes early diagnosis, and programs to ensure early diagnosis are costly.
(E) The net savings in medical resources achieved by some preventive health measures are smaller than the net losses attributable to certain other measures of this kind.Reasoning:
Here we are just looking at the cost of treatment of hypertension of all the affected population versus the comparatively lower costs incurred by of a fraction of the people who really suffer the strokes etc. We are not seeing the enormous cost savings from the economic losses that would have arisen, had these populations continued to suffer due to not treating the hypertension. Choice A makes this clear and hence weakens the argument that there is no economic justification for preventive treatment for hypertension.
5. Percentage and absolute figure traps. In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by three percentage points over the past ten years. Since many local businesses in Florida cater to retirees, these declines are likely to have a noticeably negative economic effect on these businesses and therefore on the economy of Florida.
Which of the following, if true, most seriously weakens the argument given?
(A) People who moved from one state to another when they retired moved a greater distance, on average, last year than such people did ten years ago.
(B) People were more likely to retire to North Carolina from another state last year than people were ten years ago.
(C) The number of people who moved from one state to another when they retired has increased significantly over the past ten years.
(D) The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.
(E) Florida attracts more people who move from one state to another when they retire than does any other state.Reasoning:
The conclusion claims that eventually business for Florida retailers will go down because ther is an overall drop of 3% in inflows. But it fails to recognize that overall ther is more movement within the country of people moving from state to another, including into Florida. Now if because of the higher movement, the actual I follow in terms absolute number is more than the 3% drop, then, the retailers will all in fact have more people than before to cater to, notwithstanding he fall of 3%. Therefore the businesses that cater to Florida retirees may not shrink and may on the contrary go up. Choice C brings out the case and thus weakens the conclusion that Florida retailers catering to retirees will suffer from loss of business.
Some GMAT examples1. A drug that is highly effective in treating many types of infection can, at present, be obtained only from the bark of the ibora, a tree that is quite rare in the wild. It takes the bark of 5,000 trees to make one kilogram of the drug. It follows, therefore, that continued production of the drug must inevitably lead to the ibora’s extinction.
Which of the following, if true, most seriously weakens the argument above?
(A) The drug made from ibora bark is dispensed to doctors from a central authority.
(B) The drug made from ibora bark is expensive to produce.
(C) The leaves of the ibora are used in a number of medical products.
(D) The ibora can be propagated from cuttings and grown under cultivation.
(E) The ibora generally grows in largely inaccessible places.2. Robot satellites relay important communications and identify weather patterns. Because the satellites can be repaired only in orbit, astronauts are needed to repair them. Without repairs, the satellites would eventually malfunction. Therefore, space flights carrying astronauts must continue.
Which of the following, if true, would most seriously weaken the argument above?
(A) Satellites falling from orbit because of malfunctions burn up in the atmosphere.
(B) Although satellites are indispensable in the identification of weather patterns, weather forecasters also make some use of computer projections to identify weather patterns.
(C) The government, responding to public pressure, has decided to cut the budget for space flights and put more money into social welfare programs.
D) Repair of satellites requires heavy equipment, which adds to the amount of fuel needed to lift a spaceship carrying astronauts into orbit.
(E) Technical obsolescence of robot satellites makes repairing them more costly and less practical than sending new, improved satellites into orbit.3. A new law gives ownership of patents—documents providing exclusive right to make and sell an invention—to universities, not the government, when those patents result from government-sponsored university research. Administrators at Logos University plan to sell any patents they acquire to corporations in order to fund programs to improve undergraduate teaching.
Which of the following, if true, would cast the most doubt on the viability of the college administrators’ plan described above?
(A) Profit-making corporations interested in developing products based on patents held by universities are likely to try to serve as exclusive sponsors of ongoing university research projects.
(B) Corporate sponsors of research in university facilities are entitled to tax credits under new federal tax-code guidelines.
(C) Research scientists at Logos University have few or no teaching responsibilities and participate little if at all in the undergraduate programs in their field.
(D) Government-sponsored research conducted at Logos University for the most part duplicates research already completed by several profit making corporations.
(E) Logos University is unlikely to attract corporate sponsorship of its scientific research.4. The difficulty with the proposed high-speed train line is that a used plane can be bought for one-third the price of the train line, and the plane, which is just as fast, can fly anywhere. The train would be a fixed linear system, and we live in a world that is spreading out in all directions and in which consumers choose the freewheel systems (cars, buses, aircraft), which do not have fixed routes. Thus a sufficient market for the train will not exist.
Which of the following, if true, most severely weakens the argument presented above?
(A) Cars, buses, and planes require the efforts of drivers and pilots to guide them, whereas the train will be guided mechanically.
(B) Cars and buses are not nearly as fast as the high-speed train will be.
(C) Planes are not a free-wheel system because they can fly only between airports, which are less convenient for consumers than the high speed train’s stations would be.
(D) The high-speed train line cannot use currently underutilized train stations in large cities.
(E) For long trips, most people prefer to fly rather than to take ground-level transportation.5. “Life expectancy” is the average age at death of the entire live-born population. In the middle of the nineteenth century, life expectancy in North America was 40 years, whereas now it is nearly 80 years. Thus, in those days, people must have been considered old at an age that we now consider the prime of life.
Which of the following, if true, undermines the argument above?
A) In the middle of the nineteenth century, the population of North America was significantly smaller than it is today.
(B) Most of the gains in life expectancy in the last 150 years have come from reductions in the number of infants who die in their first year of life.
(C) Many of the people who live to an advanced age today do so only because of medical technology that was unknown in the nineteenth century.
(D) The proportion of people who die in their seventies is significantly smaller today than is the proportion of people who die in their eighties.
(E) More people in the middle of the nineteenth century engaged regularly in vigorous physical activity than do so today.
“Better than a thousand days of diligent study is one day with a great teacher” – a Japanese proverb.