GMAT Math : Data Sufficiency

GMAT Math : Data Sufficiency 

 Question

 How must is 60 percent of a certain number

Statement 1 : 25 percent of twice the number is equal to half the number.
Statement 2 : 50 percent of the number is 20 less than the number.

A) If statement 1 alone is sufficient to answer the question, but statement 2 alone is not sufficient.
(B) If statement 2 alone is sufficient to answer the question, but statement 1 alone is not sufficient.
(C) If both statements together are needed to answer the question, but neither statement alone is sufficient.
(D) If either statement by itself is sufficient to answer the question.
(E) If not enough facts are given to answer the question.

Solution:

 Answer B

Evaluating Statement 1: 25 percent of twice the number is equal to half the number.

 To determine what is 60 of a certain number (say x), you need to know what the value of that number (x) is. Statement 1 seems to provide that equation to solve for the value of x, but when you read this statement closely it is bogus leads you nowhere.

it states as
2 (0.25x ) = 0.5x
0.5x = 0.5x

You cannot solve for the value of x.

 Evaluating Statement 2: 50 percent of the number is 20 less than the number. 

 The Equation for this statement will be

0.5x = x-20
This implies,
x-0.5x= 20
Solving for 
0.5x =20
x=40

Since we know the value of X we can now find 60 percent of x.
So the correct choice is answer B

GMAT Math Practice - Coordinate Geometry

GMAT Math Practice - Coordinate Geometry 

Question

Line P is described by the equation 3x + 2y - 4 = 0.  Which of the following lines is parallel to P and has the same x-intercept as the line  5x - y + 5 = 0?
a) 6x = -5y + 20
b) -y = (3/2)x +20
c)  -4x - 6y =8
d)  y = -3x - 3
e) - 4y = -6x-12

Solution

 For some reason, many GMAT test takers seem to be confused with such a question and they immediately start by plotting points on the axes.

 You need to know simple rule for parallel lines.

Lines are parallel when they have the same slopes, and the slope is easiest to see when a line is written in slope intercept from y = mx + b.

Converting P to that form we get
y = -3x + 4 or
y = -3x + 4
So the slope of any parallel line will be -3. The second condition is given by the 2nd equation.  Its x-intercept is the x-value where y = 0.

That is 5x - 0 + 5 = 0
5x = -1 so
x = -1 .

For each of the given answer choices, we can start by looking for either a matching slope or x-intercept, and then if it matches one, see if it matches both.

Answer D is y = -3 x - 3.

y = -(3)x -3

Therefore the slope is -3, and parallel to P.  Furthermore, substituting in x = -1.y = -3 x -3

y = 3 - 3 = 0 

So this line also has the desired x intercept.

Sentence Correction - Practice Question

Sentence Correction - Practice Question

Question

The National space probe recently published a report cautioning that many of the space rubble to which satellites and spacefaring vessels are exposed pose a significant risk of damaging or destroying satellites and vessels in instances of accidental impact.

a) many of the space rubble to which satellites and spacefaring vessels are exposed pose

b) many of the space rubble that satellites and spacefaring vessels are exposed to poses

c) many of the rubble that is in space and that satellites and spacefaring vessels are exposed to pose
d) much of the rubble that is in space and satellites and spacefaring vessels are exposed to poses

e) much of the space rubble to which satellites and spacefaring vessels are exposed poses

Solution

Answer D

 

This is a easy rule to remember and a sure short question that helps a GMAT test taker can score a point. 

“Much” and “many” are commonly confused words. “Many” is right for countable quantities and is plural; “much” is correct when discussing unquantifiable amounts and is singular. Since it would be virtually impossible for someone to try to count space rubble, this sentence should contain “much.”

And since "much" is singular, its verb should be, too ("poses"). But be careful: even though "much is singular, "satellites and spacefaring vessels" is a compound-- and therefore plural-- noun, so "are exposed" is correct. Now choose the option that is clear, concise, and correct. 

 

Introduction to Critical Reasoning on GMAT

Introduction to Critical Reasoning on GMAT

The focus of the critical reasoning Questions on the GMAT test is test how good are you in analyzing fact sets from a bunch of lines. On, age, you have 1 minute and 45 seconds to complete each question. So sometimes the pressure goes really high when the paragraph is little longer or when the paragraph is to confusing. The GMAT is a structured test so it will test you on a predictable pattern. In critical reasoning, there are certain question types that are tested again and again.

A typical GMAT critical reasoning Question

Every critical reasoning question that you see on the GMAT will have three parts to it:

1) The Stimulus,

2) The Question Stem, and

3) The Options

Now that you know the structure of an actual GMAT Question on the GMAT test, you are ready to know what are the components of an argument.

Components of an Argument

Every argument in a critical reasoning question on the GMAT test has three pasts.

1) Evidence or stated facts

2) Conclusion

3) Assumptions

You need to remember that

EVIDENCE + ASSUMPTION leads to (=) CONCLUSION.

Almost every question will be missing the ASSUMPTION part, that is the test takers will have to analyze the assumption based on the evidence and conclusions. Sometime, it may also happen that the stimulus will be just a collection of facts and no conclusion will be provided. In such cases, it will be most likely that the question stem will ask you to find the conclusion from the options.

Assumption

The stimulus will usually appear in two forms - as an argument or as several statements of facts and the hidden assumption. You need to understand that assumptions are a critical part of GMAT critical reasoning. Just think it in this way, every author who ever writes an article or an argument is always based on some prior assumption that he or she makes.

For example:

In response to the increasing cost of producing energy through traditional means, many utility companies have begun investing in renewable energy sources, chiefly wind and solar power, hoping someday to rely on them completely and thus lower energy costs. As one can easily see, these sources will be less risky for the utilities than nonrenewable sources, such as gas, oil, and coal, whose prices can fluctuate dramatically according to availability.

So what do you think is the assumption behind this argument. Here are few assumptions on which this argument could be based on:

(i) Running cost is low or negligible in using renewable energy sources

(ii) One can predict weather patterns

Conclusion

Always start by reading the stimulus. Some students prefer reading the question stem first but I see that as waste of time because you will read the question stem, then read the stimulus and then habitually read the question steam again. You should take an average of two minutes to answer each critical reasoning question. This is an average and not hard and fast rule. Some questions may take more and some may take less.

GMAT Math: Word Problem - Set Theory

GMAT Math: Word Problem - Set Theory

 In a village of hundred households, 75 have at least one DVD player, 80 have at least one cell phone, and 55 have at least one MP3 player. Every village has at least one of these three devices. If X and Y are respectively the greatest and the lowest possible number of households that have all the three of these devices, X-Y is :

A) 65

B) 55

C) 45

D) 35

E) 25

Solution

Answer C

This is a really tricky one, you will encounter this on the actual GMAT if you are doing very good on the GMAT math section. This involves sets.

First we need to figure out what the maximum is. We know it is possible there are 55 with all three, since the 55 MP3 owners is smallest set of the three. (Max = # of MP3)

To calculate the fewest possible, we first need to figure out how many must have all three devices. (max possible - max without all three = minimum with all three).

Of the 80 cell phone owners, 25 cannot have an MP3 player 80 - 55 = 25.

Similarly, 20 of the DVD owners cannot have an MP3 player. 75 - 55 = 20.

If the owners who do not have all three are unique (no overlap), we get the maximum number of owners who do not own an MP3 player, and thus cannot own all three devices.

Max possible - maximum without all three = minimum number of people with all three devices.

55 - 45 = 10

Now we can solve:

55 - 10 = 45.

Sentence Correction Practice Question

Sentence Correction Practice Question

Question

Found on several Indian subcontinent, Bengal Tigers dominate their habitat, and grow to lengths of up to 6 feet, running swiftly enough that deer and wild boar serve as its primary live prey.

A) Bengal Tigers  dominate their habitat, and grow to lengths of up to 10 feet, running swiftly enough

B Bengal Tigers dominate their habitat and grow to lengths of up to 10 feet, and with such swift running

C) Bengal Tigers dominate their habitat and grow to lengths of up to 10 feet, they run swiftly enough

D) the Bengal Tiger dominates its habitat, growing to lengths of up to 10 feet and running so swiftly

E) the Bengal Tiger dominates its habitat, grows to lengths of up to 10 feet, and it runs swiftly enough

Solution

Answer D

This sentence contains errors in pronoun agreement. The plural “Bengal Tigers” and the referent "their" do not agree with the singular “its” in the non-underlined section of the sentence. Therefore, “Bengal Tigers” must be replaced by the singular “Bengal Tiger” and "their" by "its." Next, the present participle form of a verb (-ing) is appropriate when the word or phrase is used as an adjective or in an adjectival phrase, so "growing" and "running" are preferable and appropriate since they refer to the Bengal Tiger's domination of its habitat. Finally, the phrase “running swiftly that” is not the correct idiom. The correct construction is “so x that y,” or “running so swiftly that deer…”

Sentence Correction Practice

Sentence Correction Practice

 Under the Forestry Protection Act, the Australian  Forest Service is required either to certify individual counties’ plans for managing the containment of wildfires or that they implement their  own plan for counties that lack appropriate regulation.

a) that they implement their

b) for implementing their

c) they should implement their

d) it should implement its

e) to implement its

ANSWER E

Solution

The GMAT loves prepositional parallelism.  In fact, generally, the GMAT likes to repeat the very same preposition--"with," "after," "against," whatever--to emphasize parallelism, even when they don't have as good a reason as they do here.

There are actually two ways to use the preposition "to" to accompany a list of infinitive verbs.  You can repeat the "to" with each verb: "I like to eat most of the day, to sleep most of the night, and to watch cartoons whenever I'm not eating or sleeping."  Or you can distribute the "to" over the entire list: "I like to eat most of the day, sleep most of the night, and watch cartoons whenever I'm not eating or sleeping."  On the GMAT, the credited response will almost always repeat the "to," rather than distributing it.  The only likely exceptions are when the phrases that form the list are very short, just one or two words, such as, "I like to eat, sleep, and watch cartoons."

OK, so that means we expect the word "to" to start the underlined section. 

 Only answer choice E starts with "to."

By the way, the the singular subject, “Australian Forest Service” must be referred to by a singular pronoun.

GMAT Math - Word problem; Geometry

GMAT Math - Word problem; Geometry 

Question

A circle is divided into four sections. If 3 sections constitute 1/4, 2/5, and 3/20 of its total area, what is the fractional value of the area of the 4th section?

a) 1/2

b) 1/3

c)1/4

d)1/5

e)1/6

Solution

For this one, fight the urge to draw out the circle. This isn't really a geometry question, despite the fact that it mentions a circle. It's really just a fraction question.

Add the 3 known sections of the circle's area. To do so, find the lowest common demonimator and add the fractions. 1/4 = 5/20, 2/5 = 8/20 and 3/20 The total fractional value of the 3 sections is 16/20. Therefore, the area of the 4th section must be 1 - 16/20 = 1/5.

You could also backsolve if this one's confusing. Look for the choice that, when added to the three given fractions, equals 1.

Answer is D