Number Properties - From MGMAT Question Bank

by KM Fri Oct 10, 2008 8:37 am

Sequence A is defined by the equation An = 3n + 7, where n is an integer greater than or equal to 1. If set B is comprised of the first x terms of sequence A, what is the median of set B ?

(1) The sum of the terms in set B is 275.

(2) The range of the terms in set B is 30.

I am specially looking at (2) statement. how can we assume first term is 10 ???

Pls help

-KM

by **Saurav** Sat Oct 25, 2008 3:57 pm

I am specially looking at (2) statement. how can we assume first term is 10 ???

I dont think we have to assume that A1 = 10, the question itself says that n =1,2,3,4..... and so on

Hence A1=10, A2=13, A3=16, A4=19 and so on...

by **JonathanSchneider** Thu Nov 13, 2008 1:35 am

Saurav's reply is correct. We have been given the rule for the sequence, where "A" represent the value of any term, and "n" represents the number in the sequence of that term. So, A(sub1) = the value of the first term = 3(1)+7 = 10.

by **DWG** Thu Nov 13, 2008 3:55 am

Question regarding (A). Can we assume that we know whether or not x is even? That really seems to be the limiting factor on whether or not this is sufficient.

(B) seems sufficient to me.

So my answer would be either (D) -or- (B).

Can someone help me with my question?

Thanks

by **kylo** Thu Nov 13, 2008 8:03 am

i think we cant assume here that the first term is 10.
if the first term starts when n=2, then first term will be 13. This will still satisfy the condition given above in the question.

hence IMO E.

Thanks!

by **ahistegt4** Sun Nov 23, 2008 8:21 am

I think, the first n terms means n=1, 2, 3, etc.
Hence, answer is D

by **JonathanSchneider** Thu Dec 11, 2008 3:27 am

Again, go back to Saurva's point. We know that n can be "greater than or equal to one." n, by the way, is a specific letter used for sequences to represent the number of the term in the sequence. The first term is always n = 1.

by **netcaesar** Sun Jan 11, 2009 6:22 pm

Is the OA A?

For 2) we have several cases...and for that reason is NOT SUFF

by **JonathanSchneider** Fri Feb 13, 2009 3:02 pm

The answer is actually D. Be careful. We know that Set A looks like this:

10, 13, 16, 19, 22, 25, 28, 31, 34, 37, 40 ...

Now, Set B contains the FIRST X terms in Set A.

As a result, when Statement 2 tells us that we have a range of 30, we simply need to see that we go from 10 up to 40. This is sufficient.

You would of course be correct that (2) would be insufficient had we not been told that Set B contains the FIRST X terms. But that word "first" is very important here.

Number Properties - From MGMAT Question Bank

Number Properties - From MGMAT Question Bank

Re: Number Properties - From MGMAT Question Bank