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# For a finite series of nonzero numbers, the number of

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Intern
Joined: 04 Nov 2007
Posts: 48
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Kudos [?]: 3 [0], given: 0

For a finite series of nonzero numbers, the number of [#permalink]  10 Nov 2007, 10:42
For a finite series of nonzero numbers, the number of variations in sign is defined as the number of pairs of consecutive terms of the sequence for which the product of the 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
VP
Joined: 08 Jun 2005
Posts: 1147
Followers: 6

Kudos [?]: 126 [0], given: 0

variations in sign is defined as the number of pairs of consecutive terms of the sequence for which the product of the two consecutive terms is negative.

In English --->

In a set the product of the two consecutive terms is negative (i.e -1*1 = -1 but 1 and -1 are not consecutive or 1*2 = 2 consecutive but this is not negative)

in the list 1,-3,2,5,-4,-6 you have

2*-3 = -6
-4*5 = -20
5*-6 = -30
-3*4 = -12

Intern
Joined: 04 Nov 2007
Posts: 48
Followers: 0

Kudos [?]: 3 [0], given: 0

Correction [#permalink]  10 Nov 2007, 11:13
KillerSquirrel wrote:
variations in sign is defined as the number of pairs of consecutive terms of the sequence for which the product of the two consecutive terms is negative.

In English --->

In a set the product of the two consecutive terms is negative (i.e -1*1 = -1 but 1 and -1 are not consecutive or 1*2 = 2 consecutive but this is not negative)

in the list 1,-3,2,5,-4,-6 you have

2*-3 = -6
-4*5 = -20
5*-6 = -30
-3*4 = -12

KillerSquirrel,

I like the way you translated the question. The correct answer is C. You got it all right until you multiplied -3*4. There is no positive 4 in the sequence. So, the answer is 3 variations.

Thanks for the explanation
VP
Joined: 08 Jun 2005
Posts: 1147
Followers: 6

Kudos [?]: 126 [0], given: 0

Yes , you are correct.
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# For a finite series of nonzero numbers, the number of

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