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medenica: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Fri Jan 05, 2007 6:28 pm; Followed by:1 members

GMATPrep Test 1 - DS Sequence

by medenica » Thu Jan 11, 2007 10:55 pm

If the terms of a squence are t1, t2, t3, ... , tn, what is the value of n?

1) The sum of the n terms is 3,124
2) The average of the n terms is 4

1 and 2 together are sufficient but can someone actually work out the problem? What are the formulas through which n is derived?

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Source: Beat The GMAT — Problem Solving | Thu Jan 11, 2007 10:55 pm

Argen: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Sun Jan 07, 2007 6:14 pm; Thanked: 1 times

by Argen » Thu Jan 11, 2007 11:17 pm

2) suggests that 4 = (sum of n terms) / n
1) states that (sum of n terms) = 3124
Therefore n = (sum of n terms) / 4 = 3124 / 4 = 781

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medenica: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Fri Jan 05, 2007 6:28 pm; Followed by:1 members

by medenica » Thu Jan 11, 2007 11:43 pm

Oh wow... how embarrassing. I was really complicating things - it's funny how missing what's being asked for does that...

tnx!

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Wed Jun 20, 2018 4:28 pm

medenica wrote:If the terms of a squence are t1, t2, t3, ... , tn, what is the value of n?

1) The sum of the n terms is 3,124
2) The average of the n terms is 4

We need to determine the number of terms in the sequence.

Statement One Only:

The sum of the n terms is 3,124.

Since we don't know anything about each individual term, we can't determine the number of terms in the sequence. Statement one alone is not sufficient.

Statement Two Only:

The average of the n terms is 4.

Since we don't know anything about each individual term, we can't determine the number of terms in the sequence. Statement one alone is not sufficient.

Statements One and Two Together:

Since sum = quantity x average, we have:

3,124 = n x 4

n = 3,124/4 = 781

Answer: C

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