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smokers and drinkers

by sanju09 » Wed Aug 25, 2010 9:56 pm
In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

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by aloneontheedge » Wed Aug 25, 2010 10:05 pm
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
IMO C
make a box with smokers and drinkers,non smokers and non drinkers
stmnt 1: 120 people were drinkers no other info insuff
stmnt 2:doesnt help u either.
combining 120 were drinkers and 40% of it will give u the answer
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by sanju09 » Wed Aug 25, 2010 10:14 pm
aloneontheedge wrote:
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
IMO C
make a box with smokers and drinkers,non smokers and non drinkers
stmnt 1: 120 people were drinkers no other info insuff
stmnt 2:doesnt help u either.
combining 120 were drinkers and 40% of it will give u the answer
how could 40 percent of drinkers answer the stem, can you please show your cards?
The mind is everything. What you think you become. -Lord Buddha



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by aloneontheedge » Wed Aug 25, 2010 10:37 pm
sanju09 wrote:
aloneontheedge wrote:
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
IMO C
make a box with smokers and drinkers,non smokers and non drinkers
stmnt 1: 120 people were drinkers no other info insuff
stmnt 2:doesnt help u either.
combining 120 were drinkers and 40% of it will give u the answer
how could 40 percent of drinkers answer the stem, can you please show your cards?
drinkers nondrinkers total
smokers X
non smokers
120(stem1) 30=(150-120) 150
clearly stmtn 1 is not suff
stmnt 2 is not suff either
combining 40 percent of the smokers were drinkers also(marked as X) which is 0.4*120=48
hope this is clear.i do not know how to draw.If you tried attempting this using venn diagram,it wud have been complicated
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by sanju09 » Wed Aug 25, 2010 11:05 pm
aloneontheedge wrote:
sanju09 wrote:
aloneontheedge wrote:
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
IMO C
make a box with smokers and drinkers,non smokers and non drinkers
stmnt 1: 120 people were drinkers no other info insuff
stmnt 2:doesnt help u either.
combining 120 were drinkers and 40% of it will give u the answer
how could 40 percent of drinkers answer the stem, can you please show your cards?
drinkers nondrinkers total
smokers X
non smokers
120(stem1) 30=(150-120) 150
clearly stmtn 1 is not suff
stmnt 2 is not suff either
combining 40 percent of the smokers were drinkers also(marked as X) which is 0.4*120=48
hope this is clear.i do not know how to draw.If you tried attempting this using venn diagram,it wud have been complicated
Venn diagram is the only time saving and safer way to solve this problem, which we are not really supposed to on DS though, but as a matter of fact, the idea to arrive at a decision A through E whatever, must not be deceptive, otherwise the choice could be wrong in most of the cases, as in this case.

In Set language

n (D) = 120, and n (D & S) = 0.40 X n (S) is the golden question here. Although, we have

n (D & S) = n (D) + n (S) - n (D or S) = 120 + n (S) - 150

or n (D & S) = n (S) - 30, can we figure out n (S)?
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by aloneontheedge » Wed Aug 25, 2010 11:08 pm
sanju09 wrote:
aloneontheedge wrote:
sanju09 wrote:
aloneontheedge wrote:
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
IMO C
make a box with smokers and drinkers,non smokers and non drinkers
stmnt 1: 120 people were drinkers no other info insuff
stmnt 2:doesnt help u either.
combining 120 were drinkers and 40% of it will give u the answer
how could 40 percent of drinkers answer the stem, can you please show your cards?
drinkers nondrinkers total
smokers X
non smokers
120(stem1) 30=(150-120) 150
clearly stmtn 1 is not suff
stmnt 2 is not suff either
combining 40 percent of the smokers were drinkers also(marked as X) which is 0.4*120=48
hope this is clear.i do not know how to draw.If you tried attempting this using venn diagram,it wud have been complicated
Venn diagram is the only time saving and safer way to solve this problem, which we are not really supposed to on DS though, but as a matter of fact, the idea to arrive at a decision A through E whatever, must not be deceptive, otherwise the choice could be wrong in most of the cases, as in this case.

In Set language

n (D) = 120, and n (D & S) = 0.40 X n (S) is the golden question here. Although, we have

n (D & S) = n (D) + n (S) - n (D or S) = 120 + n (S) - 150

or n (D & S) = n (S) - 30, can we figure out n (S)?
that is wat i have done it but in a box which avoids much of calculation. Its all abt perception.i feel box method works much quicker for me
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by sanju09 » Wed Aug 25, 2010 11:14 pm
aloneontheedge wrote: that is wat i have done it but in a box which avoids much of calculation. Its all abt perception.i feel box method works much quicker for me
But how can we answer the stem without knowing n (S) here? I personally agree with C, but your assumption that 40 percent of n (D) will give us the answer seems fishy
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by Stuart@KaplanGMAT » Wed Aug 25, 2010 11:35 pm
sanju09 wrote:In a survey of 150 persons, how many were smokers and drinkers?

(1) 80 percent of the person surveyed were drinkers.

(2) 40 percent of the smokers were drinkers also.

[spoiler]Source: Crack-GMAT
www.crack-GMAT.com[/spoiler]
We want the number of people who belong to both groups, smokers and drinkers.

(1) gives us the number of drinkers, but nothing about smokers: insufficient, eliminate A and D.

(2) doesn't give us any actual numbers: insufficient, eliminate B.

Together: we know that 40% of the smokers are also drinkers, but we don't know what percent of the drinkers are smokers; since we only have information about the number of drinkers, we still can't answer the question: choose E.

We could also pick numbers to show that we can get multiple answers.

From (1), we know that we have 120 drinkers.
From (2), we know that 40% of the smokers are drinkers. We could have:

10 smokers, 4 of whom are drinkers, so the answer would be "4"; or
20 smokers, 8 of whom are drinkers, so the answer would be "8".

Since we can generate multiple answers, we can't answer the question - even together, insufficient.

(We can't make any assumptions in DS - nowhere does it say that all 150 had to be smokers or drinkers or both.)
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by sanju09 » Wed Aug 25, 2010 11:44 pm
Let me quote myself to continue from there, please
In Set language

n (D) = 120, and n (D & S) = 0.40 X n (S) is the golden question here. Although, we have

n (D & S) = n (D) + n (S) - n (D or S) = 120 + n (S) - 150

or n (D & S) = n (S) - 30, can we figure out n (S)?
Yes, we can figure out n (S), see how

Since, n (D & S) = 0.40 X n (S), therefore

n (S) - 30 = 0.40 X n (S), [spoiler]hence C, only if 150 are either smokers or drinkers.[/spoiler].
The mind is everything. What you think you become. -Lord Buddha



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by Stuart@KaplanGMAT » Wed Aug 25, 2010 11:46 pm
sanju09 wrote:Let me quote myself to continue from there, please
In Set language

n (D) = 120, and n (D & S) = 0.40 X n (S) is the golden question here. Although, we have

n (D & S) = n (D) + n (S) - n (D or S) = 120 + n (S) - 150

or n (D & S) = n (S) - 30, can we figure out n (S)?
Yes, we can figure out n (S), see how

Since, n (D & S) = 0.40 X n (S), therefore

n (S) - 30 = 0.40 X n (S), [spoiler]hence C[/spoiler].
No, E is really the correct answer to the question.

Please explain why the two possible answers I provide can't both be true based on the information given.

Remember, it's possible that some people are neither smokers nor drinkers.
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by sanju09 » Wed Aug 25, 2010 11:49 pm
Please read under spoiler too, it reads E, otherwise
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by Stuart@KaplanGMAT » Wed Aug 25, 2010 11:55 pm
sanju09 wrote:Please read under spoiler too, it reads E, otherwise
I don't see that anywhere in the post, but I'll take your word for it!
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by sanju09 » Thu Aug 26, 2010 12:20 am
Under the spoiler was written: [spoiler]C, only if 150 are either smokers or drinkers; otherwise E is always true[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



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by aloneontheedge » Thu Aug 26, 2010 12:34 am
sanju09 wrote:Under the spoiler was written: [spoiler]C, only if 150 are either smokers or drinkers; otherwise E is always true[/spoiler]
Since total number of drinkers are 120(i made a mistake while taking a screen shot,it reads as smokers)

x +y = 120
x = 0.4*120
hence C
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by sanju09 » Thu Aug 26, 2010 1:12 am
aloneontheedge wrote:
sanju09 wrote:Under the spoiler was written: [spoiler]C, only if 150 are either smokers or drinkers; otherwise E is always true[/spoiler]
Since total number of drinkers are 120(i made a mistake while taking a screen shot,it reads as smokers)

x +y = 120
x = 0.4*120
hence C
The point raised by Stuart Kovinsky, that we can't make any assumptions in DS - nowhere does it say that all 150 had to be smokers or drinkers or both; is sufficient to accept [spoiler]E[/spoiler] as the right answer here.

[spoiler]Let's thank him from the deepest part of our hearts now[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



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