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01 Aug 2011, 05:23
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X=(1,2,3,4,5)
Y=(-9,-8,0,1,2,3)
If an Integer is randomly selected from Set X above and an Integer is randomly selected from Set Y. What is the probability that the product of the 2 integers will be positive?
A) 0
B) 2/3
C) 2/5
D) 1/2
E) 4/5
This is how I did which obviously is wrong so plz help me find my mistake.
As the product should be +ve, we cannot include -9 and -8 from Set Y. We also cannot include 0 as anything multiplied by 0 is a 0 which is neither +ve not -ve.
So for every option in Set X we have 3 possibilities (1,2,3).
Now, while making pairs we have 1*2, 1*3 and 2*3 counted twice so we'll take one pair and will be left with the following pairs.
1*1, 1*3
2*2, 2*3
3*3
4*1, 4*2, 4*3
5*1, 5*2, 5*3
In total 11 pairs out of 11C2 (as we want 2 out of 11 numbers including -8,-9 &0)
Pls help me understand if at all i am doing right..The answer is 1/2
Y=(-9,-8,0,1,2,3)
If an Integer is randomly selected from Set X above and an Integer is randomly selected from Set Y. What is the probability that the product of the 2 integers will be positive?
A) 0
B) 2/3
C) 2/5
D) 1/2
E) 4/5
This is how I did which obviously is wrong so plz help me find my mistake.
As the product should be +ve, we cannot include -9 and -8 from Set Y. We also cannot include 0 as anything multiplied by 0 is a 0 which is neither +ve not -ve.
So for every option in Set X we have 3 possibilities (1,2,3).
Now, while making pairs we have 1*2, 1*3 and 2*3 counted twice so we'll take one pair and will be left with the following pairs.
1*1, 1*3
2*2, 2*3
3*3
4*1, 4*2, 4*3
5*1, 5*2, 5*3
In total 11 pairs out of 11C2 (as we want 2 out of 11 numbers including -8,-9 &0)
Pls help me understand if at all i am doing right..The answer is 1/2
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01 Aug 2011, 08:15
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Since you have only positive integers in set X, the integers in set Y will make the product either positive or negative.
So no matter which integer you pick from X, for the purpose of probability you can take the following pairs:
X*(-9) = Negative
X*(-8) = Negative
X*0 = 0, no positive
X*1 = Positive
X*2 = Positive
X*3 = Positive
X being any integer from the X set. You could write out all the pairs, picking one integer from X and other from Y, but that is not necessary.
So you have 6 pairs, and 3 positive results. 3/6 = 1/2. Answer is D.
So no matter which integer you pick from X, for the purpose of probability you can take the following pairs:
X*(-9) = Negative
X*(-8) = Negative
X*0 = 0, no positive
X*1 = Positive
X*2 = Positive
X*3 = Positive
X being any integer from the X set. You could write out all the pairs, picking one integer from X and other from Y, but that is not necessary.
So you have 6 pairs, and 3 positive results. 3/6 = 1/2. Answer is D.
01 Aug 2011, 08:35
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cano
You are assuming Set X to have only one number wherein it has 5 numbers..don't we need to multiply all the numbers in Set X with each and every number in Set Y to find out the +ve value??
