Banning cigarette advertisements in the mass media will not reduce the

Can someone explain? How should I tackle these weaken questions, they always wound me up.

Also, what is the conclusion here, the last sentence or the first? I thought it to be the last sentence. Please explain.

Thank You.

I'm pretty sure the first sentence is the main conclusion and the last sentence would probably be a supporting conclusion. Try to think about what the main message the argument is trying to make when deciding.

When in doubt between 2 sentences, try this method that @e-gmat teaches to determine which one is the conclusion.
Try to CAUSALLY link (with the use of "BECAUSE") the 2 statements in both directions. For example :

In this passage, the 2 sentences are :
A. Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke
B. They do not need the advertisements to supply that information

First CAUSAL link :
<Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke> BECAUSE <They do not need the advertisements to supply that information>

Second CAUSAL link (Other way round) :
<They do not need the advertisements to supply that information> BECAUSE <Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke>

See which one of the above 2 linkages makes sense in the context of the argument.

Obviously the first link does.
Whatever comes before the BECAUSE in the correct link is the conclusion of the argument.
Therefore, for this passage, <Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke> is the CONCLUSION of the argument.

Takes a bit of getting used to, but this method really works well for complex arguments.

gauranggarg, there are a few ways to test for a conclusion if you are confused. The easiest and best way? Do the because/therefore test. This helps test for premises/conclusions or sub conclusions/conclusions. It has been explained above, but I just want to add a little more to the explanation.

Here's how it works:

Because Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke. They know that cigarettes exist and they know how to get them. Therefore They do not need the advertisements to supply that information.

Therefore Banning cigarette advertisements in the mass media will not reduce the number of young people who smoke. They know that cigarettes exist and they know how to get them. Because They do not need the advertisements to supply that information.

Now, of the two sentences above, which is the correct one? The second one. Because they do not need to do something, it will not have an effect; the last supports the first. The "because" is the support, and will always be a premise/sub conclusion, whereas the therefore, which is a conclusion indicator, is our conclusion. This is the best way to go about solving this issue. From a logic perspective, a premise is just support. If you have to ask yourself "Why?" after a statement, you know that this is a conclusion. If you need to support it, it is a conclusion.

Seeing or hearing an advertisement for a product tends to increase people’s desire for that product.

clearly if there will be less advertisement , then they will be less desired to smoke. hence weakning conclusion.

This is the quick solution I came up with:

Conc: Banning cigarette ads in the mass media will not reduce the number of young people who smoke, i.e., ads can't be used as a variable to control smoking.

(A) Seeing or hearing an advertisement for a product tends to increase people’s desire for that product. - This pretty much answers the question straight out of the gate. "Do ads or exposure to ads impact smoking tendencies in the population?" If the ads lead to higher desire for a product (which we already know how to obtain) then removing those same ads might reset the baseline for desire to lower level, a.k.a reduce desire and reduce smoking levels. Keep

(B) Banning cigarette advertisements in the mass media will cause an increase in advertisements in places where cigarettes are sold - This option pretty much says that removing ads will lead to more ads promoting cigarettes. However, we're already told that cigarette ads don't have an effect in the passage. The reasoning provided here challenges the facts rather than the assumption. Drop

(C) Advertisements in the mass media have been an exceedingly large part of the expenditures of the tobacco companies - How much money a tobacco company spend on ads seems pretty inconsequential to the passage. Granted companies can be spending huge sums, but doesn't weaken the reasoning that ads can't be used as a variable to control smoking levels. Drop

(D) Those who oppose cigarette use have advertised against it in the mass media ever since cigarettes were found to be harmful. - This shifts the conversation from banning ads to advertising against it. This can be used to create an unsupported story as follows - In the absence of ads promoting cigarettes, the ads against cigarette usage will reduce smoking among young people. Hence, banning cigarette ads will have the intended effect. However, we're already told that ads don't work, i.e., people already know where and how to obtain cigarettes, so the above can't be concluded either. Drop

(E) Older people tend to be less influenced by mass-media advertisements than younger people tend to be. - This actually strengthens the conclusion. Drop­

­Experts! Gmat ninja, karishma, AndrewN ... please tell why option E is wrong ? As Media advertisement affects more younger people , so if cigarette advertisements is banned in media , then it should definitely reduce the number of young people who smoke.  I need a reason how we can say it irrelevant comparison or out of scope. 
Thanks