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

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Intern
Joined: 04 Nov 2007
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For a finite series of nonzero numbers, the number of [#permalink]

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10 Nov 2007, 11:42
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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
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10 Nov 2007, 11:55
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

the answer is (D)

Intern
Joined: 04 Nov 2007
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10 Nov 2007, 12:13
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

the answer is (D)

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: 1145
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Kudos [?]: 213 [0], given: 0

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10 Nov 2007, 12:17

Yes , you are correct.
10 Nov 2007, 12:17
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# For a finite series of nonzero numbers, the number of

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