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by Tutor » Fri Mar 07, 2014 3:31 am
sgr21 wrote:Find the missing term in the series represented by?

5,28,57,88,125, ?
Hi sgr21,

If you look at the difference between any two consecutive term, it turns out to be a series we get by adding consecutive prime numbers:
28-5 = 23
57-28= 29
88-57= 31
125-88= 37

Going by this logic, to get the next term, we should add the next prime number i.e., 41.
So the next term should be 125+41 = 166

Now GMAT does test the concept of Series and Sequences and Prime Numbers, I am not very sure if this an official GMAT question.
Nevertheless, I hope you got your answer.

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by GMATGuruNY » Fri Mar 07, 2014 3:46 am
sgr21 wrote:Find the missing term in the series represented by?

5,28,57,88,125, ?
Not a GMAT problem.
If the GMAT asks us to find the value of a missing term, a formula for the sequence will be provided.
That said, the sequence above seems to conform to the following pattern:
5+23 = 28.
28+29 = 57.
57+31 = 88.
88+37 = 125.

The values in the red are consecutive prime numbers, in ascending order.
After 37, the next greatest prime number is 41.
Thus, the next term after 125 should be as follows:
125+41 = 166.
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by Brent@GMATPrepNow » Fri Mar 07, 2014 8:02 am
sgr21 wrote:Find the missing term in the series represented by?

5,28,57,88,125, ?
As the others have mentioned, the GMAT does not test our ability to find missing terms in a sequence unless the sequence is defined for us. The reason is that there's no way that we can definitively determine ONE (and ONLY ONE) pattern in a given sequence.

Consider this example: 1, 2, 4, __
What's the missing term here?
Well, if we read the sequence as doubling from one term to the next, the next term is 8
HOWEVER, if we notice that we keep adding successively larger integers to each term (i.e., add 1, then add 2, then add 3, etc.) the next term is 7

Likewise, (if we want to get a bit silly), we might look at the given sequence (5, 28, 57, 88, 125, __) and say that the missing term is 88. Why?
Because 5 is my favorite number, 28 is my 2nd favorite number, 57 is my 3rd favorite number, ... and 88 is 6th favorite number.

So, rest assured, you won't be required to find missing terms on a GMAT sequence, unless the sequence is defined for us.

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by [email protected] » Fri Mar 07, 2014 2:41 pm
Hi sgr21,

Everyone else in this thread has properly explained the sequence and that it does NOT fit the style nor the presentation of how the GMAT would present a sequence question. While you will be tested on your basic understanding of prime numbers and sequences, it won't be in this way.

You should make sure to stay focused on GMAT-specific material as you continue your GMAT prep.

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