Ask me Anything about GMAT Data Sufficiency https://gmatclub.com/forum/download/file.php?id=52844 Hello and welcome to GMAT preparation. You may know me from GMATBusters' Quant Quiz . I hope you are finding the Quiz very useful. This topic is a new feature on the DS Forum and a way for you to directly interact with me and ask anything about the DS (even PS ), e.g. if you want a certain concept explained or have a particular you question you want me addressed, this is the place to post a link to it or your question. If you have any doubts/queries about Quant DS (even PS ), I would be happy to address them. If the question is general in nature regarding strategy or any concept , you can post it here . you can tag me in a post to ask queries related to the particular question. Participate in the Quiz , we will discuss the Quiz questions in the webinar here . Join the chat group -GMAT Busters, I would be conducting Quant doubt sessions every Saturday 9PM EST. Here is the Chat group link Bookmark and follow this post to get the updates Happy Learning!!!

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shameekv1989

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18 Apr 2020, 08:21

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Hi,
It can be done by finding the concentration at each step, but as the new solution added is not 0% milk, it will affect the new concentration differently each step.

Step 1)

3L of the solution is drawn from a container containing 30L of solution that is 20% concentrated. It is replaced by another solution that is 10% concentrated
it is same as mixing 2 solutions:
i) 27L of 20% and 3L of 10%
final concentration will be : (27*.2+3*.1)/30 = 0.19 or 19%

Step 2)

3L of the new solution is drawn from a container containing 30L of solution that is 19% concentrated. It is replaced by another solution that is 10% concentrated
it is same as mixing 2 solutions:
i) 27L of 19% and 3L of 10%
final concentration will be : (27*.19+3*.1)/30 = 0.181 or 18.1%

Step 3)

3L of the new solution is drawn from a container containing 30L of solution that is 18.1% concentrated. It is replaced by another solution that is 10% concentrated
it is same as mixing 2 solutions:
i) 27L of 18.1% and 3L of 10%
final concentration will be : (27*.181+3*.1)/30 = 0.1729 or 17.29%

Since, in this question, the pattern will not be there, and we need to calculate each step individually, it is highly unlikely that the question with more than 2 steps will be asked in GMAT.

I Hope, the concept is clear.

Feel free to tag me in case of any doubt.

Happy Learning.

shameekv1989

Hello, I have a question regarding "3L of milk are drawn from a container containing 30L of milk. It is replaced by water and the process is repeated 2 times. What is the ratio of milk to water at the end?"

Solution to this is concentration after 3 rounds :- (1 - 3/30)^3 = 721/1000 (Because in each round the concentration for the previous round changes and eventually turns out to be this in the end)

However, I wanted to understand how can I extend this concept to much harder or rather complicated questions for eg:-

3L of solution is drawn from a container containing 30L of solution that is 20% concentrated. It is replaced by another solution that is 10% concentrated and the process is repeated 2 times. What is the concentration of solution after 3 rounds?

Thanks in advance,
Shameek

Wow!! Thanks, you made it look pretty simple. I think you can use the same thinking for other replacement mixture problems as well right?

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18 Apr 2020, 08:31

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Yes, it can be applied to other mixture replacement problems as well.

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My first real GMAT test is tomorrow, almost 24 hours exactly from when I'm writing this. I just finished one of the practice exams on the GMAT website and scored a 730(Q45 V44 IR7). This is way above my target score, which makes me feel confident I have the material down well enough to do well on the exam.

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08 May 2020, 06:37

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All the best for the exam tomorrow.

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08 May 2020, 07:21

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Best wishes for your exam.

For today

Don't overstrain yourself today.
What hasn't sunk in by now won't magically lodge itself in your brain overnight.
Do finish studying early. Take the evening off to do something fun and relaxing.
Do get a good night's rest.

During Test:

Do stay optimistic. If the questions seem too difficult, that might actually be a good sign as your score is dependent on the difficulty level you manage to get from the algorithm. Stay calm, work quickly but methodically without rushing or jumping into conclusions.
Don't let any single question take you out of your pace or focus.

Be confident you will get a good score. Do share your test experience with us.

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11 Jun 2020, 22:58

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The GMAT Quantitative section contains two types of questions, Problem Solving and Data Sufficiency. ... You don't need to give the answer to the actual question. You just have to decide whether either statement (or both statements) gives data that is sufficient for finding an answer—hence the term data sufficiency

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18 Oct 2020, 06:52

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How often does functions appear on GMAT

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19 Oct 2020, 06:09

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One can expect 1-2 questions on function but that doesn't mean that one can leave this topic as this topic is the basis of higher-order problems of other topics too.

Chetanjalan

How often does functions appear on GMAT

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Register for the online webinar on the coming Sunday.
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30 Oct 2020, 00:32

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Is $m*k^4$ > 0?
1) $m^2-8m+15<0$
2) $k^2-6k+8>0$

Looking at the question we realise that , for the equation to be positive or negative we just need to know whether m is positive or negative.
Because k is raised to an even power , k doesnt play any role in the sign of the expression.

solving statement 1
we get m<5 and m<3
this is not sufficient as we dont know whether m is positive or -ve.

statement 2
insufficient as no info about m is provided

there fore none of the statements are sufficient

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30 Oct 2020, 09:38

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Hi

Hope your query has been resolved

Chetanjalan

How often does functions appear on GMAT

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What is the number of 360 degree rotations that a bicycle wheel made while rolling 250 meters in a straight line without slipping?

i) The diameter of the bicycle wheel, including the tire, is 0.6 meters.
ii) The wheel made twenty 360 degree rotations per minute.

The first statement is totally true and there is no problem about that. However the answer says that the second one is not sufficient. Could you explain why is that?

Thanks in advance, stay healthy!

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The wheels needs to travel 250m
we need to find in how many rotations, we know in one rotation (one complete rotation = 360 deg rotation), the wheel will cover the distance = circumference.
hence, n = total distance to be traveled /distance covered in one rotation
hence we need circumference.

St1) Dia is known, hence circumference is known. Sufficient
St2) The wheel made twenty 360 degree rotations per minute. but since we don't know the distance traveled in one rotation, it is NOT sufficient.
Suppose if the wheel is very small, say of size of a coin, it has to make many revolution.
but if the wheel is very BIG, only a few revolution.

Hence , the Time factor has no role to play, We need the circumference,

NOT Sufficient.

Answer A

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13 Nov 2020, 03:59

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In an ordered list of integers, is the average equal to the median?

S-1) The range of the integers in the list is 1.5 times the median.
S-2) Each integer in the list after the first is equal to the sum of the preceding integer plus a constant k.

Can anybody help on the above question :

I Have questions about S-1 being sufficient - as consider list : 1,3 ,5 ,7 , here Range = 1.5 times median , and median = mean , so is this solution wrong as given by Princeton

As per Princeton Review answer is D)

This is a Yes/No Data Sufficiency question, so Plug In. The task of a Yes/No Data Sufficiency is to determine whether the information in the statements produces a consistent Yes or No response for any number that satisfies the statement(s). Evaluate the statements one at a time.

Evaluate Statement (1), which says that the range of integers in the list is 1.5 times the median. If the list is 1, 3, 6, 8, 10, then the statement is satisfied because the range (10 – 1 = 9) is 1.5 times the median (6), and the average (, or 5.6) is not equal to the median (6), so the answer to the question is “No.” Now, Plug In again to determine whether there is a way to produce a “Yes” answer. If the list is 2, 3, 4, 5, 8, then the statement is satisfied because the range (8 – 2 = 6) is 1.5 times the median (4), and the average (, or 4.4) is not equal to the median (4), so the answer to the question is “No.” In fact, for any list of integers that satisfies Statement (1), the average will not equal the median, so the answer will consistently be “No” and therefore the statement is sufficient. Write AD.

Now evaluate Statement (2), which says that each integer in the list after the first is equal to the sum of the preceding integer plus a constant k. If the list is 1, 3, 5, 7, 9, then the statement is satisfied because each number in the list after the first equals the preceding integer plus constant 2, and the average of the list (, or 5) equals the median of the list (5), so the answer to the question is “Yes.” Now, Plug In again to determine whether there is a way to produce a “No” answer. If the list is 3, 6, 9, 12, 15, then the statement is satisfied because each number in the list after the first equals the preceding integer plus constant 3, and the average of the list (, or 9) equals the median of the list (9), so the answer to the question is “Yes.” If fact, for any list of integers that satisfies Statement (2), the average of the list will equal the median, so the answer will consistently be “Yes,” and therefore the statement is sufficient. Eliminate choice A. The correct answer is choice D.

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16 Nov 2020, 04:53

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Hi yes you are right, St 1 is NOT sufficient.

list : 1,3 ,5 ,7 , here Range = 1.5 times median , and median = mean .
So, we are also getting answer "YES "

hence not sufficient to answer the question uniquely.

Deepakjhamb

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From 2000 to 2003 the number of employees at a certain company increased by a factor of 1/4. From 2003 to 2006 the number of employees at this company decreased by a factor of 1/3. If there were 100 employees at the company on 2006, how many employees were there at the company in 2000 ?

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23 Dec 2020, 11:12

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Is it a PS Question or DS Question?

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23 Dec 2020, 21:47

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Is it a PS Question or DS Question?

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Let the number of employees on 2000 = x
the number of employees on 2003 = x(1+1/4)= 5x/4
the number of employees on 2006 = 5x/4 * (1-1/3)=5x/4 * 2/3 = 5x/6
Now. 5x/6 = 100
x = 600/5 = 120

Hence, the number of employees on 2000 = 120

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