Here is what the argument says:

- Washing machines are teeming with bacteria that can cause infections.
- Rinsing these machines with bleach (note that it doesn't say concentrated bleach/diluted bleach and doesn't talk about the amount of bleach to be added) gets rid of such bacteria.
- However concentrated bleach can severely corrode the metal drum in the machines.

Conclusion: Thus, diluted bleach is an effective and safe means of eliminating any health risks from such washing machines.

There are various questions that can be raised to weaken the conclusion.
At what level of dilution is the bleach effective and safe?
Is bacteria the only health risk in the washing machines?
Does the beach itself leave deposits in the machine and create health risks?

Option (A) says that the machines have many other pathogens. We don't know whether the bleach is effective on them or not. Hence, we cannot say that bleach will eliminate all health risks. Hence it weakens the conclusion.

B. Undiluted bleach is not more powerful than diluted bleach in killing bacteria.
It tells us that diluted bleach is effective (and safe). Hence it strengthens our conclusion.

C. Many companies come with gentle bleach blends that do not corrode the metal drum of the household washing machines.
Irrelevant. It tells us that suitably diluted bleach is available.

D. Various studies have shown that certain bacteria can live outside the human body for long periods of time on various objects such as clothes, toys etc.
Gives more information about the first sentence of the argument. Has no connection to the conclusion that bleach is effective in eliminating all health risks.

E. Most household washing machines come with a hot-water cycle that is set at a temperature of 90 degrees Celsius, a temperature that has been cited as ideal for killing various disease-causing bugs in these machines.
Gives another method of eliminating health risks. Does not weaken that bleach in effective in eliminating health risks.

Answer (A)
_________________

Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

A (IMHO) the argument says "effective means of eliminating any health risks from such washing machines", not just bacteria, so even when you kill bacteria with wtvr bleach you use, health is still endangered by other harmful means aka pathogens.

narmadadhruv

Choice E deals with bugs, not bacteria... aren´t you assuming they both pose the same threat?

Regards,

Thanks for pointing that out! But the other in option A troubles me.

Regards,
Dhruva

This is very comprehensive, but I think that your questions will be answered, so please bear with me.

A. Studies have shown that besides bacteria, many other kinds of pathogens can be found in regularly used washing-machines.

Within scope - "any health risks" is the conclusion drawn by the author. Such a generalization would find weakness by introducing health risks other than that caused by bacteria. Do we know that bleach kills these other pathogens? Since we must take this answer choice as true, it brings considerable doubt and/or questions to whether bleach can eliminate any health risks, and the author's conclusion is hasty and insufficiently supported.

This is the answer.


B. Undiluted bleach is not more powerful than diluted bleach in killing bacteria.

This may sound as if it weakens, but it's irrelevant. It may require the author to modify the conclusion to say that either diluted or undiluted bleach will be effective in killing bacteria... in fact, I argue that the author doesn't even have to modify the conclusion, as the author only makes a claim in the conclusion with respect to diluted bleach (yes, the argument brings up details about undiluted bleach causing damage to washing machine drums, but the conclusion is about how extreme that info is interpreted - e.g. restate the conclusion "only with respect to diluted bleach, we can conclude X").

Anyway, the point still remains that undiluted bleach will still cause damage to the machine. Thus, you'd still want to use diluted bleach instead of undiluted bleach, as the author suggests.

C. Many companies come with gentle bleach blends that do not corrode the metal drum of the household washing machines.

This actually strengthens the author's argument. It's similar to restating the info that's already mentioned, as gentle bleach blends is a type of diluted bleach. It's not irrelevant - if undiluted bleach seriously damages washing machine drums, then diluted bleach's effects on washing machine drums cannot be inferred. So, the author makes a leap in concluding that diluted bleach is safe for machines.

Also, as a very minor aside, if diluted bleach wasn't available (e.g. "there are no bleach blends..."), it would be equivalent to suggesting a magical solution, as if-then logic dictates that any false hypothetical can be followed by a true or false conclusion, making the entire logical equation true (e.g. if it rains chocolate outside everyday, then I am a billionaire = true statement)! Then it seriously undermines the author's conclusion because blends or diluted bleach may not be available for purchase for use in washing machines, making the author's solution ineffective and entirely irrelevant. Thus, with the wording changed, choice C would be the answer, as bleach cannot be used to kill any bacteria, and will knock out the actual answer to this question, which at least kills some bacteria even if more pathogens are introduced (unavailable bleach effectively eliminates no health risks vs., bleach eliminates some or possibly even all health risks, respectively).

D. Various studies have shown that certain bacteria can live outside the human body for long periods of time on various objects such as clothes, toys etc.

This only adds to the given info with very little value-added. This answer choice reinforces the background detail to generate more support for the author's conclusion. Conclusion: Use diluted bleach... Author's support: because washing machines transfer bacteria onto clothes, which... Answer Choice D: "Various studies have shown that certain bacteria can live outside the human body for long periods of time on various objects such as clothes, toys etc."...

E. Most household washing machines come with a hot-water cycle that is set at a temperature of 90 degrees Celsius, a temperature that has been cited as ideal for killing various disease-causing bugs in these machines.

This may sound as if bleach is unnecessary, but the point still remains... if the hot-water cycle is sufficient at killing various disease-causing bugs, which is indeed a health risk, then are other disease causing sources eliminated? It's confined to just disease-causing bugs and does not necessarily pertain to bacteria, or any other health risks for that matter. In fact, it can be used to support the conclusion, in that the hot-water cycle can combine with the diluted bleach to eliminate (more, not necessary any and all) health risks. Does it weaken or support the author's conclusion? Clearly, this answer choice has commitment issues.

strongly feel that I have seen this question before. Anyways, some of the options are too far fetched and hence easy to eliminate.
Hope I will improve in the next 2 months.

bleach, as long as it is diluted properly, is an effective means of eliminating any health risks from such washing machines, with no harmful effects on these machines

Marked above is the conclusion, given this, any option that suggests that
1.) diluted bleach does not corrode
2.) diluted bleach does kill all harmful bacteria should strengthen the arg.; negation of which shall weaken it.

A.->talks about another entity; even if we were to consider this option, we are assuming that pathogens are harmful.
B.-> strengthens
c. -> Close to pre-thinking options (mentioned above)
D.-> strengthens
E.-> somewhat like A; in that it introduces another entity.

Rgds,
Dhruva

Studies have shown that regularly used household washing machines are teeming with bacteria that find their way onto our clothes and consequently onto us, causing various bacterial infections. Rinsing these machines with bleach is an effective way to get rid of such bacteria. However, certain other studies have shown that bleach, when used in the undiluted form, can severely corrode the metal drum in the machines. Thus, bleach, as long as it is diluted properly, is an effective means of eliminating any health risks from such washing machines, with no harmful effects on these machines.

Which of the following, if true, weakens the argument above?

Scope Shift: The argument talks about bacteria and its health threats, but concludes about 'any health risks'. We need to expose this.

A. Studies have shown that besides bacteria, many other kinds of pathogens can be found in regularly used washing-machines. - Perfect.

B. Undiluted bleach is not more powerful than diluted bleach in killing bacteria.

C. Many companies come with gentle bleach blends that do not corrode the metal drum of the household washing machines.

D. Various studies have shown that certain bacteria can live outside the human body for long periods of time on various objects such as clothes, toys etc.

E. Most household washing machines come with a hot-water cycle that is set at a temperature of 90 degrees Celsius, a temperature that has been cited as ideal for killing various disease-causing bugs in these machines.

Binit.