Sequencing A for B

[jthollenbach]

I was not sure which forum to post this question to, so it might have to be moved.

This comes from the number properties question bank. The question states:
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.


Explanation:
(2) SUFFICIENT: The first term of set B is 10. If the range is 30, the last term must be
10 + 30 = 40. The mean of the set then must be (10 + 40)/2 = 25. This is sufficient.

my question is in regards to the explanation for (b), how can we assume that the first number in the set is 10, or n=1. It does not state this in the question stem, it simple states that n is a integer greater or equal to 1. This being said, I would think if the first term was n=20 and the last n=50, the range would be 30 and the median would be much higher.

Please let me know if i am missing something. Thanks.

Tyler

[saurav.raaj]

The set b contains FIRST x terms, hence n=1, kind of written indirectly.

I was not sure which forum to post this question to, so it might have to be moved.

This comes from the number properties question bank. The question states:
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 ?

[JonathanSchneider]

Yes, Saurav's got it. But this phrasing is not indirect; it's actually very typical.

Note that "n" in the sequence definition is the "number in that sequence;" hence the first number in the sequence has n = 1.