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GMAT CLUB'S FRESH CHALLENGE QUESTION:

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 04:08

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49 B. 12/49 C. 13/49 D. 18/49 E. 24/49 -------------- Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7 For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 04:25

Munch wrote:

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49 B. 12/49 C. 13/49 D. 18/49 E. 24/49 -------------- Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7 For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 04:30

kablayi wrote:

Munch wrote:

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49 B. 12/49 C. 13/49 D. 18/49 E. 24/49 -------------- Total number of ways is 7*7 =49

Number of ways to select 1 number from A --> 7C1 -->7 For the product to be negative select a positive number from B > no.of ways --> 3c1 -- >3

Total possibility -- > 7 *3 -- 21

Probability is 21/49

But i am not able to find the answer in the question stem

]The question specifically asks for integers,

Oh ya!! thanks!! then it should be 8 .. I doubled checked the possibility to match the answer, but still missed the word integer..

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 05:28

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

I am not sure whether we should consider the product numbers of ‘0’.

Considering ‘0’ as an eligible possibility, A X B will be -ve when, either A or B is -ve. Since all values for A is -ve, then all values of B must be +ve. In such case, only pairs will be -ve when value of B is 1/5 , 1/3 or 1/2. For each A, there will be 3 Negative Values, i.e A X B = -10*1/5 = -10/5 ; -10/3 ; -10/2 = -9/5 ; -9/3 ; -9/2 . . . and so on.

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 06:04

1

This post received KUDOS

The question specifically asks for -ve integers("0" is not a -ve integer). Now Set A has only -ve integers so we have to select only +ve fractions from set B i.e.{1/5,1/3,1/2}. With 1/5 we can only select -10 & -5 from set A. So possible combinations : 1/5*-10 & 1/5*-5. Number of possible combinations = 2

With 1/3 we can only select -9 & -6 from set A. Number of possible combinations = 2 With 1/2 we can only select -10,-8,-6,-4 from set A. Number of possible combinations = 4 Thus we have 2+2+4 = 8 combinations Total Possible combinations = 7C1 * 7C1 = 49 Ans = 8/49

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49 B. 12/49 C. 13/49 D. 18/49 E. 21/49

Since we are looking for negative integer, we have to consider only POSITIVE numbers in set B as all are NEGATIVE in set A.. 1) 1/2 This will give integers when multiplied by MULTIPLE of 2 So -4,-6,-8,-10......4ways 2) 1/3 Similarly when multiplied by MULTIPLE of 3 -6,-9.....2ways 3) 1/5 When multiplied by MULTIPLE of 5 So -5,-10.....2ways

Re: If a number is to be randomly selected from set A above and a number [#permalink]

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13 Dec 2017, 18:59

chetan2u wrote:

Bunuel wrote:

GMAT CLUB'S FRESH CHALLENGE QUESTION:

A = {-10, -9, -8, -7, -6, -5, -4} B = {-1/2, -1/3, -1/5, 0, 1/5, 1/3, 1/2}

If a number is to be randomly selected from set A above and a number is to be randomly selected from set B above, what is the probability that the product of the two numbers will be a negative integer?

A. 8/49 B. 12/49 C. 13/49 D. 18/49 E. 21/49

I missed the INTEGER PART

Since we are looking for negative integer, we have to consider only POSITIVE numbers in set B as all are NEGATIVE in set A.. 1) 1/2 This will give integers when multiplied by MULTIPLE of 2 So -4,-6,-8,-10......4ways 2) 1/3 Similarly when multiplied by MULTIPLE of 3 -6,-9.....2ways 3) 1/5 When multiplied by MULTIPLE of 5 So -5,-10.....2ways