Seminar attendance prob

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon May 24, 2010 1:11 am

GMAT PREP

At a two day seminar ,90 percent of those registered attended the seminar on the first day
what percent of those registered did not attend the seminar on either day?

A) A total of 1000 people registered for the two day seminar

B) Of those registered, 80 percent attended the seminar on second day

Pls suggest

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Source: Beat The GMAT — Data Sufficiency | Mon May 24, 2010 1:11 am

liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Mon May 24, 2010 1:23 am

From 1
we get 100 people did not attended the seminar on day 1,but no information on how many attended on day 2...not sufficient

From 2
we get 80% of registered attended on day 2,but no in formation on how many of the registered people attended both days..not sufficient

combining ,
does not provide any of the missing information..not sufficient

IMO ans option E

"If you don't know where you are going, any road will get you there."
Lewis Carroll

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon May 24, 2010 1:38 am

Pls correct me if I am wrong

Combining A and B we get

Day 1 -

total registerd - 1000

Attended - 900 Not attended - 100

Day2-

Total registered -1000

Attended - 800 Not attended -200

So combining A and B we r getting the result

Pls clarify

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liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Mon May 24, 2010 1:44 am

selango wrote:Pls correct me if I am wrong

Combining A and B we get

Day 1 -

total registerd - 1000

Attended - 900 Not attended - 100

Day2-

Total registered -1000

Attended - 800 Not attended -200

So combining A and B we r getting the result

Pls clarify

As I have mentioned ,none of the options provide any informations on how many attended on both days

ex, let 700 attended on both days

in day 1 900 attended and 100 didnt
day 2 800-700=100 attended who didn't attended day 1

so all who have registered have attended at least one day..ans is 0%

Now take 800 attended on both days
in day 1 900 attended and 100 didnt
day 2 800-800=0 attended who didn't attended day 1

so in this case ans is 100 or 10%

we need to know how many people(percentage) attended the seminar both days to ans this question.

"If you don't know where you are going, any road will get you there."
Lewis Carroll

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon May 24, 2010 1:54 am

We need people who did not attend the seminar on either day

Day 1 - 100

Day 2 - 200

Total 300 people did not attend the seminar on either day

So 300 is 30 % of 1000 people

pls clarify

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liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Mon May 24, 2010 2:02 am

selango wrote:We need people who did not attend the seminar on either day

Day 1 - 100

Day 2 - 200

Total 300 people did not attend the seminar on either day

So 300 is 30 % of 1000 people

pls clarify

check the line in bold. That is not correct.correct statement is 'Total 300 people did not attend the seminar on either 1 or day 2 ' .People didn't attended on either day means people who have not attended on both days not any one of the days.
Does this clarifies?
btw what is the OA?

"If you don't know where you are going, any road will get you there."
Lewis Carroll

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon May 24, 2010 2:07 am

oops got it

Thanks

Answer is E

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Patrick_GMATFix: GMAT Instructor; Posts: 1052; Joined: Fri May 21, 2010 1:30 amFollowed by: 98 members; Thanked: 335 times

by Patrick_GMATFix » Mon May 24, 2010 11:36 am

This is GMATPrep question 1441. Please watch the step-by-step video solution if you still have trouble solving.

-Patrick

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[email protected]: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Mon Apr 26, 2010 9:30 pm; Location: Johannesburg, South Africa

by [email protected] » Tue May 25, 2010 3:22 am

selango wrote:GMAT PREP

At a two day seminar ,90 percent of those registered attended the seminar on the first day
what percent of those registered did not attend the seminar on either day?

A) A total of 1000 people registered for the two day seminar

B) Of those registered, 80 percent attended the seminar on second day

Pls suggest

use the sets theory to solve this problem!!

here there are two sets that intersect: people who attended Day1 only, Day2 only and people who attended both days.

let T = total of all registered,
let z = people who attended both Day1 and Day2
let x = people who attended Day1 only then x = 0.9T - z
let y = people who attended Day2 only;

therefore, people who did attend neither days = 1000 - (x+y+z)

Statement 1:

T = 1000
x= 900 - z

insufficient

Statement 2:

y = 0.8T - z

insufficient

combine statements 1 & 2:
x = 900 - z
y = 800 - z

1000 - (x+y+z) = 1000 - (1700 - z) = z - 700

insufficient

here neither statement alone will get you an answer not the combination of both statements (i.e. C).

ANSWER is (E)

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