Hey Guys,Please help me with this one.

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dddanny2006: Master | Next Rank: 500 Posts; Posts: 209; Joined: Thu Jan 12, 2012 12:59 pm

by dddanny2006 » Tue Nov 05, 2013 12:47 am

How many members of Group G are less than 25 years of age?

(1)Exactly 3/5 of the members of Group G are 25 years of age or older.
(2)The 24 men in Group G constitute 30 percent of the groups membership.

I know the answer,but my doubt is why cant we assume a particular number for G.I assumed it to be 100 and that does give us the answer. A lot of time's on the GMAT,I've come across stuff that says assumptions should be made,but that's not consistent to all the problems.Why is assumption not the right way to go about in this problem?

Thanks

I also seem to be making mistakes in problems like these

If p3>= -125 and p is an integer,what is the value of p?

(1) 3p+16<=4
(2)p2 >16

I know the answer to this problem too,but I did make a mistake when solving it.
Where can I get more problems like these for practice?Any online links.

Thank you

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Source: Beat The GMAT — Data Sufficiency | Tue Nov 05, 2013 12:47 am

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by [email protected] » Tue Nov 05, 2013 1:07 am

Hi dddanny2006,

For the first question, you can TEST Values to figure out whether each Fact is sufficient or insufficient. Here's how:

We're asked HOW MANY members of Group G are less than 25 years old?

Fact 1: 3/5 of Group G are 25 or OLDER.

This means that 2/5 of Group G are younger than 25. BUT, this doesn't give us the actual number....

If the TOTAL group = 5, then 2/5 = 2
If the TOTAL group = 10, then 2/5 = 4
Since the answers differ, Fact 1 is INSUFFICIENT

Fact 2: 24 men in Group G = 30% of the total membership.

This means that 24 = .3(total)
So, the total = 80, but we DON'T KNOW how many are less than 25 years old.
Fact 2 is INSUFFICIENT

Combined, we know there are 80 members AND 2/5 are younger than 25 years old.
(2/5)(80) = 32, so we have the only possible answer
Together, SUFFICIENT

Final Answer: C

For the second question, you've admitted to making a silly mistake. THOSE silly mistakes, if you make too many of them, will keep you from scoring at the level that want to be scoring at. Fix those mistakes and your score will increase.

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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mevicks: Master | Next Rank: 500 Posts; Posts: 269; Joined: Thu Sep 19, 2013 12:46 amFollowed by: 7 members; Thanked: 94 times

by mevicks » Tue Nov 05, 2013 11:02 pm

dddanny2006 wrote:How many members of Group G are less than 25 years of age?
(1)Exactly 3/5 of the members of Group G are 25 years of age or older.
(2)The 24 men in Group G constitute 30 percent of the groups membership.

If everything was provided in percentages (or ratios or fractions) then we could have easily used a smart number such as 100. Since the question asks about the "Number" of people in the group we can't use a smart number here. However we can still go ahead and use percentages in our Double Matrix table:

Q: Number of people less than 25 = ?

St1:

We cannot find the number of members, so INSUFFICIENT

St2:
No of men in the group = 24
% representation of men = 30%

30% of Total = 24
Thus total number of members = 2400/30 = 80

Modified table with actual numbers (instead of percentages):

Again, no way to find out the Number of people less than 25, so INSUFFICIENT

St1+2:
Total = 80
60 % of 80 can be found out, so SUFFICIENT

Answer : C

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mevicks: Master | Next Rank: 500 Posts; Posts: 269; Joined: Thu Sep 19, 2013 12:46 amFollowed by: 7 members; Thanked: 94 times

by mevicks » Tue Nov 05, 2013 11:12 pm

dddanny2006 wrote: ...
Where can I get more problems like these for practice?Any online links.

The materials provided by the GMAC are the best source for "tricky" GMAT problems... If you have exhausted a material move on to another

https://www.mba.com/Store/Store-catalog. ... CAT2680001

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed Nov 06, 2013 4:45 am

dddanny2006 wrote:How many members of Group G are less than 25 years of age?

(1)Exactly 3/5 of the members of Group G are 25 years of age or older.
(2)The 24 men in Group G constitute 30 percent of the groups membership.

Do not SOLVE.
Determine only whether there is SUFFICIENT information to solve.

Statement 1:
Tells us only that 2/5 of the members are less than 25 years of age.
No way to determine the actual NUMBER of members less than 25 years of age.
INSUFFICIENT.

Statement 2:
Since the 24 men are equal to 30% of the total number of members, the total number of members can be determined.
No way to determine how many of these members are less than 25 years of age.
INSUFFICIENT.

Statements combined:
Statement 2 gives us the total number of members.
Statement 1 tells us that 2/5 of these members are less than 25 years of age.
Thus, the number of members less than 25 years of age can be determined.
SUFFICIENT.

The correct answer is C.

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