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Finite Sequence !!!

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by kop » Wed Nov 13, 2013 6:55 am
For a finite sequence of non zero numbers, the number of variations in sign is defined as the number of pairs of consecutive terms of sequence for which the product of two consecutive terms is negative. what is the number of variations in sign for the sequence 1,-3,2,5,-4,-6 ?

a. one
b. two
c. three
d. four
e. five

Please help me understand the question. :shock:
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by Brent@GMATPrepNow » Wed Nov 13, 2013 7:09 am
kop wrote:For a finite sequence of non zero numbers, the number of variations in sign is defined as the number of pairs of consecutive terms of sequence for which the product of two consecutive terms is negative. what is the number of variations in sign for the sequence 1, -3, 2, 5, -4, -6 ?

a. one
b. two
c. three
d. four
e. five
We're asked to look at every pair of consecutive terms. If the product of that pair is negative, this counts as one variation.

Let's examine the pairs of consecutive terms:

1 and -3: product is negative
-3 and 2: product is negative
2 and 5: product is positive
5 and -4: product is negative
-4 and -6: product is positive

Since 3 pairs of consecutive terms have negative products, the correct answer is C

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by [email protected] » Wed Nov 13, 2013 5:21 pm
Hi kop,

The GMAT Quant section usually includes at least one "symbolism" question that will either "make up" a math symbol and ask you to perform a calculation with it OR make up a math phrase/concept and ask you to use the concept to answer a question.

These questions are essentially about following instructions.

Here, we're asked to take the PRODUCT of TWO CONSECUTIVE terms. If the product is NEGATIVE, then we have a "variation." So, given the included sequence of numbers, how many "variations" are there? As Brent has already shown, you would need to work through every pair of consecutive terms, and you would find 3 "variations."

These types of questions can sometimes take a little time to solve, but are some of the easiest "math" questions on the exam.

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by fifafreak » Thu Nov 14, 2013 5:22 am
kop wrote:For a finite sequence of non zero numbers, the number of variations in sign is defined as the number of pairs of consecutive terms of sequence for which the product of two consecutive terms is negative. what is the number of variations in sign for the sequence 1,-3,2,5,-4,-6 ?

a. one
b. two
c. three
d. four
e. five

Please help me understand the question. :shock:
the number of variations in sign = number of pairs of consecutive terms of sequence for which the product of two consecutive terms is negative.
Start finding the products of consecutive nos. in the above sequence. no. of negative products is our answer. hope that helps.

1*(-3) ; 2*(-3) ; 5*(-4)
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