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Numbers Question

This topic has 4 expert replies and 0 member replies
aditiniyer Senior | Next Rank: 100 Posts
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19 Aug 2016
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46 messages

Numbers Question

Post Wed Mar 08, 2017 10:26 am
A school administrator will assign each student in a group on n students to one of m classes.If 3
1) It is possible to assign each of the 3n students to one of m classes so that each classroom has the same number of students assigned to it.

2)It is possible to assign each of the 13n students to one of m classes so that each classroom has the same number of students assigned to it.

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Post Wed Mar 15, 2017 10:18 pm
aditiniyer wrote:
A school administrator will assign each student in a group on n students to one of m classes.If 3
1) It is possible to assign each of the 3n students to one of m classes so that each classroom has the same number of students assigned to it.

2)It is possible to assign each of the 13n students to one of m classes so that each classroom has the same number of students assigned to it.
Hi aditiniyer,

We already have great solutions to the question. Here's my take on this question...

We have to see if n/m is an integer.

Let's take each statement one by one.

S1: It is possible to assign each of the 3n students to one of m classes so that each classroom has the same number of students assigned to it.

=> (3n)/m = 3*(n/m) is integer.

Say 3*(n/m) = k; where k in a positive integer

=> n/m = k/3

If k = 4, n/m is not an integer. The answer is NO.

If k = a multiple of 3, n/m is an integer. The answer is YES. No unique answer.

S2: It is possible to assign each of the 13n students to one of m classes so that each classroom has the same number of students assigned to it.

=> (13n)/m = 13*(n/m) is integer.

13*(n/m) = k; where k in a positive integer

In order to get k, a positive integer, either m is a multiple of 13 or k is a multiple of 13. But we are given that m < 13, so it's not possible. Thus, k must be a multiple of 13, making n/m an integer. Sufficient.

The correct answer: B

Hope this helps!

-Jay
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If k = a multiple of 3, n/m is an integer. The answer is YES. No unique answer.

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GMAT/MBA Expert

Post Wed Mar 15, 2017 3:31 pm
aditiniyer wrote:
A school administrator will assign each student in a group on n students to one of m classes.If 3
1) It is possible to assign each of the 3n students to one of m classes so that each classroom has the same number of students assigned to it.

2)It is possible to assign each of the 13n students to one of m classes so that each classroom has the same number of students assigned to it.
We are given that each student in a group of n students is going to be assigned to one of m classrooms. We are being asked whether it is possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students.

Thus, we need to determine whether n/m = integer.

Statement One Alone:

It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.

Statement one is telling us that 3n is evenly divisible by m. Thus, 3n/m = integer.

However, we still do not have enough information to answer the question. When n = 16 and m = 4, n/m DOES equal an integer; however, when n = 20 and m = 6, n/m DOES NOT equal an integer.

Statement Two Alone:

It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

This statement is telling us that 13n is divisible by m. Thus, 13n/m = integer.

What is interesting about this statement is that we know that n is greater than 13 and that m is less than 13 and greater than 3. Thus, we know that m could equal any of the following: 4, 5, 6, 7, 8, 9, 10, 11, or 12. We see that none of those values (4 through 12) will divide evenly into 13.

Knowing this, we can say conclusively that m will never divide evenly into 13. Thus, in order for m to divide into 13n, m must divide evenly into n.

Answer: B

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GMAT/MBA Expert

Post Wed Mar 08, 2017 3:49 pm
Quote:
A school administrator will assign each student in a group of n students to one of m classrooms. If 3 < m < 13 < n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?

(1) It is possible to assign each of 3n students to one of m classrooms so that each classroom
has the same number of students assigned to it.

(2) It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.
Target question: Is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it

This is a great candidate for rephrasing the target question (more info about rephrasing the target question can be found in this free video:
http://www.gmatprepnow.com/module/gmat-data-sufficiency?id=1100)

In order to be able to assign the same number of students to each classroom, the number of students (n) must be divisible by the number of classrooms (m). In other words, n/m must be an integer.

REPHRASED target question: Is n/m an integer?

Statement 1: It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students to it.
This statement is telling us that the number of students (3n) is divisible by the number of classrooms (m). In other words, 3n/m is an integer.
Does this mean mean that m/n is an integer? No.
Consider these contradictory cases.
case a: m = 4 and n = 20, in which case n/m is an integer.
case b: m = 6 and n = 20, in which case n/m is not an integer.
Since we cannot answer the REPHRASED target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students to it
This statement tells us that the number of students (13n) is divisible by the number of classrooms (m). In other words, 13n/m is an integer.

The given information tells us that 3 < m < 13 < n. Since m is between 3 and 13, there's no way that 13/m can be an integer. In fact, we can't even reduce the 13/m to simpler terms. From this, we can conclude that n/m must be an integer.
Since we can answer the REPHRASED target question with certainty, statement 2 is SUFFICIENT

Answer = B

For even more information on rephrasing the target question, you can read this article I wrote for BTG: http://www.beatthegmat.com/mba/2014/06/30/rephrasing-the-target-question

Cheers,
Brent

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GMAT/MBA Expert

Post Wed Mar 08, 2017 10:36 am
Quote:
A school administrator will assign each student in a group of n students to one of m classrooms. If 3 < m < 13 < n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?

(1) It is possible to assign each of 3n students to one of m classrooms so that each classroom
has the same number of students assigned to it.

(2) It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.
To assign the same number of students to each classroom, the number of students (n) must be divisible by the number of classrooms (m).

Question rephrased: Is n/m an integer?

Statement 1: It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.
In other words, the number of students (3n) is divisible by the number of classrooms (m).
Implication:
(3n)/m = 3(n/m) = integer.

Case 1: n/m = integer
It's possible that n=16 and m=4, with the result that n/m = 16/4 = 4.
Here, 3(n/m) = 3(16/4) = 12.

Case 2: n/m = k/3, where k is not a multiple of 3
In this case, since n/m = k/3, m must be a multiple of 3.
It's possible that n=14 and m=6, with the result that n/m = 14/6 = 7/3.
Here, 3(n/m) = 3(7/3) = 7.

Since n/m is an integer in Case 1 but not in Case 2, INSUFFICIENT.

Statement 2: It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.
In other words, the number of students (13n) is divisible by the number of classrooms (m).
Implication:
(13n)/m = 13(n/m) = integer.

Case 3: n/m = integer
It's possible that n=16 and m=4, since 16/4 = 4.
Here, 13(n/m) = 13(16/4) = 52.

Case 4: n/m = k/13, where k is not a multiple of 13
In this case, since n/m = k/13, m must be a multiple of 13.
Not possible, since 3 < m < 13.

Since only Case 3 is possible, n/m = integer.
SUFFICIENT.

The correct answer is B.

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