school administrator - can u please check?

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school administrator - can u please check?

by maoriba » Fri Nov 26, 2010 2:22 am
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.

Solution:

(1) m=3n so 3n/m is an integer. Given that n can be any number bigger that 13, n can be 14, 15, 16, 17, 18, 19... . m can be 4, 5, 6, 7,8, 9, 10, 11, 12. If m = 10 and n=15, 3*15/10=4,5 which is not an integer, BUT if I have m=10 and n= 30, 3n/m is an integer. NOT SUFFICIENT

(2) 13n = m so 13n/m is an integer. If n =15 and m =5, 13n/m is an integer, so it s ok. BUt if n= 15 and m = 4 the ratio is not an integere. Not Sufficient.

Check together 3n = m and 13n = m.
so 3n/m = 13n/m which can only happen if n=0, but it is not possible.

I end up wioth E.
riba made
Source: — Data Sufficiency |

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by Laura GMAT Tutor » Fri Nov 26, 2010 10:43 am
You used numbers that aren't permissible when you tried statement 2.

"(2) 13n = m so 13n/m is an integer. If n =15 and m =5, 13n/m is an integer, so it s ok. BUt if n= 15 and m = 4 the ratio is not an integer. Not Sufficient." But the point is that according to statement 2, it MUST be true that 13n/m= integer. If you use 13(15)/4, that isn't an integer. That means that the numbers n=15 and m=4 are not allowed by statement (2) so you shouldn't use them to evaluate the question.

Does that help?

Be sure to keep in your mind the difference between "impermissible" values and values that lead to an answer of "no" to the original question. :)
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