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

Redeem

Ratio 2 and combined

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

Ratio 2 and combined

by karthikpandian19 » Mon Jan 09, 2012 6:37 pm
The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?

8
9
10
11
12
Top
Source: — Problem Solving |

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 » Mon Jan 09, 2012 7:30 pm
karthikpandian19 wrote:The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?

8
9
10
11
12
Given: In Class A, B : G = 3 : 4
In Class B, B : G = 4 : 5
In combined class, B : G = 17 : 22

Let the # of boys in class A = b and # of girls = g
Then in class B, # of boys = b - 1 and # of girls = g - 2
b : g = 3 : 4 implies 4b = 3g implies b = 3g/4
(b - 1) : (g - 2) = 4 : 5
5b - 5 = 4g - 8
5(3g/4) - 5 = 4g - 8
15g - 20 = 16g - 32
g = 12

The correct answer is E.

Please note that the ratio of boys and girls for combined class is irrelevant in this question.
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
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

by karthikpandian19 » Mon Jan 09, 2012 7:33 pm
Does these kind of irrelevant information comes in GMAT? becoz i have wasted more time to solve this problem wrong.
Anurag@Gurome wrote:
karthikpandian19 wrote:The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?

8
9
10
11
12
Given: In Class A, B : G = 3 : 4
In Class B, B : G = 4 : 5
In combined class, B : G = 17 : 22

Let the # of boys in class A = b and # of girls = g
Then in class B, # of boys = b - 1 and # of girls = g - 2
b : g = 3 : 4 implies 4b = 3g implies b = 3g/4
(b - 1) : (g - 2) = 4 : 5
5b - 5 = 4g - 8
5(3g/4) - 5 = 4g - 8
15g - 20 = 16g - 32
g = 12

The correct answer is E.

Please note that the ratio of boys and girls for combined class is irrelevant in this question.
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 » Mon Jan 09, 2012 7:38 pm
karthikpandian19 wrote:Does these kind of irrelevant information comes in GMAT? becoz i have wasted more time to solve this problem wrong.
Such type of questions with irrelevant information are quite rare on GMAT.
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
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 » Tue Jan 10, 2012 4:42 am
karthikpandian19 wrote:The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?

8
9
10
11
12
ALWAYS LOOK AT THE ANSWER CHOICES.

The answers choices represent the number of girls in Class A.
Since b:g = 3:4, the number of girls must be a multiple of 4.
Eliminate B, C and D.

Answer choice A: g = 8.
Since b:g = 3:4 = 6:8, b=6.
Since Class A has one more boy and two more girls than Class B, in Class B, b=5 and g=6.
Doesn't work: the required ratio in Class B is 4:5.
Eliminate A.

The correct answer is E.

Note that we had to try ONLY ONE ANSWER CHOICE and perform only SIMPLE ARITHMETIC to determine the correct answer -- a very efficient way to solve the problem.
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
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

by karthikpandian19 » Tue Jan 10, 2012 5:01 am
Thts really a short way to solve a problem less than a minute....Thanks
GMATGuruNY wrote:
karthikpandian19 wrote:The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?

8
9
10
11
12
ALWAYS LOOK AT THE ANSWER CHOICES.

The answers choices represent the number of girls in Class A.
Since b:g = 3:4, the number of girls must be a multiple of 4.
Eliminate B, C and D.

Answer choice A: g = 8.
Since b:g = 3:4 = 6:8, b=6.
Since Class A has one more boy and two more girls than Class B, in Class B, b=5 and g=6.
Doesn't work: the required ratio in Class B is 4:5.
Eliminate A.

The correct answer is E.

Note that we had to try ONLY ONE ANSWER CHOICE and perform only SIMPLE ARITHMETIC to determine the correct answer -- a very efficient way to solve the problem.
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 425
Joined: Wed Dec 08, 2010 9:00 am
Thanked: 56 times
Followed by:7 members
GMAT Score:690

by LalaB » Tue Jan 10, 2012 11:06 am
karthikpandian19 wrote:Does these kind of irrelevant information comes in GMAT? becoz i have wasted more time to solve this problem wrong.
in case if u are still interested in so- called "irrelevant info", please see below

in class A girls/total=4/7
in class B girls/total=5/9

in A+B =22/39 (so called irrelevant info)

in a q.stem it is said "Class A has one more boy and two more girls than class B". it means total of B=total of A minus 3 (one boy and 2 girls)

so, now we have the following equation -

4/7*A+5/9(A-3)=22/39(A+A-3)

A=21

Girls in A is 4/7*21=12

now we see,that everything depends on ur imagination. u can use any piece of info to solve a q.
in some cases the method above is good.
Top
User avatar
Legendary Member
Posts: 626
Joined: Fri Dec 23, 2011 2:50 am
Location: Ahmedabad
Thanked: 31 times
Followed by:10 members

by ronnie1985 » Thu Jan 12, 2012 11:39 pm
(D)
Make a table:-

Class Boys Girls
A 3x 4x
B 4y 5y
Comb 17k 22k

Also
3x = 4y+1
4x = 5y+2 and
hence, 8y+1 = 22k and 10y+2 = 22k. As first iteration k = 1, we get y = 2 and then we get Girls = 12
Follow your passion, Success as perceived by others shall follow you
Top
Master | Next Rank: 500 Posts
Posts: 382
Joined: Thu Mar 31, 2011 5:47 pm
Thanked: 15 times

by ArunangsuSahu » Fri Jan 13, 2012 12:44 pm
Better to Plug in the answer Choices.

Lot Quicker

Girls in Class A=12
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 20
Joined: Sun Oct 14, 2012 1:34 pm

by [email protected] » Sun Nov 11, 2012 1:20 pm
I solved it like this but then I get x=2 instead of 3

4/5 = 3x-1/4x-2
x=2

Can someone please explain why I get the wrong answer?

Manhattan does it like this:

3/4 = 4x+1/5x+2
x=3


Thanks!!
Top
Senior | Next Rank: 100 Posts
Posts: 52
Joined: Mon Aug 13, 2012 11:53 pm
Location: Mumbai
Thanked: 1 times

by jkaustubh » Mon Nov 12, 2012 1:42 am
[email protected] wrote:I solved it like this but then I get x=2 instead of 3

4/5 = 3x-1/4x-2
x=2

Can someone please explain why I get the wrong answer?

Manhattan does it like this:

3/4 = 4x+1/5x+2
x=3


Thanks!!
Manhattan does it like this:

3/4 = 4x+1/5x+2
x=3

what I get is x=2
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 20
Joined: Sun Oct 14, 2012 1:34 pm

by [email protected] » Thu Nov 15, 2012 7:08 am
Thanks, so it has to be an error from manhattan gmat....
Top
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Tue Jul 31, 2012 6:53 am
Thanked: 8 times
Followed by:1 members

by GaneshMalkar » Fri Nov 16, 2012 6:43 am
I dont think it is a manhattan error....

You got x = 3 for Class A and x = 2 for Class B which both are correct...
To explain it further....Class A ratio B/G = 3x/4x and x = 3 so Boys = 9 and girls = 12

Class B ratio B/G = 4x/5x and x = 2 which is Boys = 8 and Girls = 10

which satisfy both of our condition
1. Combined ratio of Class A and Class B = (8+9)/(10+12) = 17/22
2. Class A has one more boy and 2 more girls


Hope this helps....

[email protected] wrote:I solved it like this but then I get x=2 instead of 3

4/5 = 3x-1/4x-2
x=2

Can someone please explain why I get the wrong answer?

Manhattan does it like this:

3/4 = 4x+1/5x+2
x=3


Thanks!!
If you cant explain it simply you dont understand it well enough!!!
- Genius
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 20
Joined: Sun Oct 14, 2012 1:34 pm

by [email protected] » Fri Nov 16, 2012 7:42 am
You are absolutely right, I just plugged x in the wrong ratio!

Thanks
Top
Post new topic Post Reply
• Page 1 of 1