GMAT Prep 1 #3_PS Ratio #4.docx

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kwah: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Wed Jan 04, 2012 5:15 pm

by kwah » Mon Mar 19, 2012 11:24 am

I have attached a question from GMAT Prep Test 1.

What is the most efficient way to achieve this result?

Answer: D

Please advise, thank you.
K

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GMAT Prep 1 #3_PS Ratio #4.docx: (57.83 KiB) Downloaded 125 times

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Source: Beat The GMAT — Problem Solving | Mon Mar 19, 2012 11:24 am

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Mike@Magoosh: GMAT Instructor; Posts: 768; Joined: Wed Dec 28, 2011 4:18 pmFollowed by: 140 members; Location: Berkeley, CA; Thanked: 387 times

by Mike@Magoosh » Mon Mar 19, 2012 3:32 pm

Hi, there. I'm happy to help with this.

At a certain university, the ratio of the number of teaching assistants to the number of students in any course must always be greater than 3:80. At this university, what is the maximum number of students possible in a course that has 5 TAs?
(A) 130
(B) 131
(C) 132
(D) 133
(E) 134

Ratio of TA to student must be greater than 3/80. Let # of students be S. Then

5/S > 3/80

All numbers are positive, so you can cross-multiply:

5*80 > 3*S
400 > 3S

Divide by 3

400/3 = 133.333 > S

So, the biggest integer value for S is 133, answer = D.

Here's another PS question on ratios.

https://gmat.magoosh.com/questions/59

When you submit your answer for that, the next page will have the full video explanation.

Does all this make sense? Please let me know if you have any further questions.

Mike

Magoosh GMAT Instructor
https://gmat.magoosh.com/

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kwah: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Wed Jan 04, 2012 5:15 pm

by kwah » Mon Mar 19, 2012 4:19 pm

That was a good question!

Thank you Mike@Magoosh.

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Mon Mar 19, 2012 7:26 pm

kwah wrote:I have attached a question from GMAT Prep Test 1.

What is the most efficient way to achieve this result?

Answer: D

Please advise, thank you.
K

Given: Assistants : Students > 3 : 80
Assistants = 5, which implies 5 : Students > 3 : 80, then we need to find maximum no. of students.

Now 5/No. of Students > 3/80 implies No. of Students < (80 * 5)/3
So, No. of Students < 133.3 approx.
This means Maximum no. of students = 133

The correct answer is D.

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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 » Tue Mar 20, 2012 3:17 am

At a certain university, the ration of the number of teaching assistants to the number of students in any course must always be greater than 3:80. At this university, what is the maximum number of students possible in a course that has 5 teaching assistants?

1. 130
2. 131
3. 132
4. 133
5. 134

We can plug in the answer choices, which represent the number of students.
We should start with E, since the question asks for the MAXIMUM number of students possible.
When we plug in the correct answer choice, assistants/students will be greater than 3/80.

To compare fractions, cross-multiply.

Answer choice E: 134 students
5/134 > 3/80
5*80 > 3*134
400 > 402.
Eliminate E.

Answer choice D: 133 students
Is 5/133 > 3/80
5*80 > 3*133
400 > 399.
Success!

The correct answer is D.

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[email protected]: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Wed Mar 14, 2012 6:46 am; Location: Bangalore; GMAT Score:610

by [email protected] » Tue Mar 20, 2012 6:03 am

gud one again

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[email protected]: Legendary Member; Posts: 934; Joined: Tue Nov 09, 2010 5:16 amFollowed by: 14 members; Location: AAMCHI MUMBAI LOCAL; Thanked: 63 times

by [email protected] » Wed Mar 21, 2012 10:36 pm

Misinterpreted 3:80 as 3.80.

Otherwise this was a very simple question...

lost out on a lot of time because of that....

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