BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Please Help

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Wed Feb 01, 2012 9:41 pm

Please Help

by intenseCK » Wed Apr 11, 2012 2:28 am
Q1. N & Y are positive integers and 450y=n^3, which is an integer?
y/3*2^2*5
y/3^2*2*5
y/3*2*5^2
A. None
B.I
C. II
d.III
e. I, II, III

Q2- A thin piece of 40m wire is cut in two. one piece is a circle with radius r. other is a square. no wire is left over. which represents total area of circle and square in terms of r?
a. Pie r^2
b.Pie r^2+10
c. Pie r^2+1/4 Pie^2r^2
d. Pie r^2+ (40-2 pie. r)^2
e.Pie r^2+( 10-1/2pie .r)^2

Q3- if each term in the series a1+a2+......+aN is eithe 7 or 77, and the sum equals 350. which of the following cud b equal to N?
A.38
B.39
C.40
D.41
E.42

Source- GMAT Prep
Top
Source: — Problem Solving |
User avatar
Community Manager
Posts: 1060
Joined: Fri May 13, 2011 6:46 am
Location: Utrecht, The Netherlands
Thanked: 318 times
Followed by:52 members

by neelgandham » Wed Apr 11, 2012 2:39 am
Question #1 is solved here - https://www.beatthegmat.com/n-y-are-posi ... 52635.html
Question #2 is solved here - https://www.beatthegmat.com/area-of-circ ... 85340.html
Question #3 is solved here - https://www.beatthegmat.com/sum-a1-a2-a3-an-t109893.html

Please let me know if need any further help!
Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Wed Apr 11, 2012 3:39 am
intenseCK wrote:Q1. N & Y are positive integers and 450y=n^3, which is an integer?
y/3*2^2*5
y/3^2*2*5
y/3*2*5^2
A. None
B.I
C. II
d.III
e. I, II, III
450y=n^3 implies (3^2 * 5^2 * 2)y = n^3, which implies y should be 2^2 * 3 * 5 so that 450y=n^3
Then (I) will be an integer.
(II) and (III) will not be an integer always.

The correct answer is B.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Wed Apr 11, 2012 3:41 am
intenseCK wrote: Q2- A thin piece of 40m wire is cut in two. one piece is a circle with radius r. other is a square. no wire is left over. which represents total area of circle and square in terms of r?
a. Pie r^2
b.Pie r^2+10
c. Pie r^2+1/4 Pie^2r^2
d. Pie r^2+ (40-2 pie. r)^2
e.Pie r^2+( 10-1/2pie .r)^2
Perimeter of the circle = 2Ï€r
Therefore, perimeter of the square = (40 - 2Ï€r)

Hence, length of each side of the square = (40 - 2πr)/4 = (10 - πr/2)

Therefore, total area of circle and square = (Area of the circle) + (Area of the square) = πr² + (10 - πr/2)²

The correct answer is E.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Wed Apr 11, 2012 3:43 am
intenseCK wrote: Q3- if each term in the series a1+a2+......+aN is eithe 7 or 77, and the sum equals 350. which of the following cud b equal to N?
A.38
B.39
C.40
D.41
E.42

Source- GMAT Prep

Let x and y be the number of 7's and the number of 77's respectively.
Then 7x + 77y = 350 implies x + 11y = 50
x + y = 50 - 10y
So, x + y = n = 50 - 10y implies n must have the unit digit of 0 because 50 - 10y must be a number which has units digit as 0. C is the only option in which the units digit is 0.

The correct answer is C.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Wed Feb 01, 2012 9:41 pm

by intenseCK » Thu Apr 12, 2012 3:21 am
Anurag@Gurome wrote:
intenseCK wrote:Q1. N & Y are positive integers and 450y=n^3, which is an integer?
y/3*2^2*5
y/3^2*2*5
y/3*2*5^2
A. None
B.I
C. II
d.III
e. I, II, III
450y=n^3 implies (3^2 * 5^2 * 2)y = n^3, which implies y should be 2^2 * 3 * 5 so that 450y=n^3
Then (I) will be an integer.
(II) and (III) will not be an integer always.

The correct answer is B.
Hi Anurag- can u elaborate a little more as i am struggling to get your logic. why shd Y be 2^2*3*5
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Thu Apr 12, 2012 3:38 am
If n and y are positive integers and 450y = n³, which of the following must be an integer?

I. y/(3 x 2² x 5)

II. y/(3² x 2 x 5)

III. y/(3 x 2 x 5²)

a. None
b. I only
c. II only
d. III only
e. I, II, and III
450y is the cube of an integer.

When we prime-factorize the cube of an integer, we get 3 (or a multiple of 3) of every prime factor:
8 is the cube of an integer because 8 = 2³ = 2*2*2.
27 is the cube of an integer because 27 = 3³ = 3*3*3.

Thus, when we prime-factorize 450y, we need to get at least 3 of every prime factor:
450y = 2 * 3² * 5² * y

Since 450 provides only one 2, two 3's, and two 5's, y must provide the missing prime factors. We need y to provide two more 2's, one more 3, and one more 5.
Thus, the smallest possible value is y = 2² * 3 * 5.

Onto the answer choices:

I. y/(3 x 2² x 5)
(2² * 3 * 5)/(3 x 2² x 5) = 1. The smallest possible value of y yields an integer.
Eliminate every answer choice that does not include I.
Eliminate A, C and D.

II. y/(3² x 2 x 5)
(2² * 3 * 5)/(3² x 2² x 5) = 1/3. Not an integer.
Eliminate every remaining answer choice that includes II.
Eliminate E.

The correct answer is B.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Post new topic Post Reply
• Page 1 of 1