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grkmurthy
Senior Consultant
Joined: 14 Oct 2007
Posts: 37
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 Posted: Sat Jan 26, 2008 12:53 pm Post subject: Probability |
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When m and n are chosen from the sets { 1, 2, 3, 4, 5} and {6, 7, 8, 9} respectively, at random, what is the probability for m*n to be even?
(1) 1/5
(2) 1/4
(3) 5/9
(4) 3/10
(5) 7/10 |
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enigma
Associate
Joined: 21 Nov 2007
Posts: 5
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| Posted: Thu Feb 28, 2008 8:01 am Post subject: |
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The product has to be even.
so, pick one even number from the first set. probability is 2/5
pick one even number from the second set. probability is 2/4
So, combined probability is 2/5 * 2/4 = 1/5.
What is the OA? |
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ksb
GMAT Tutor
Joined: 28 Dec 2004
Posts: 54
Location: Chennai, India
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| Posted: Sun Mar 02, 2008 7:33 am Post subject: |
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| enigma wrote: | The product has to be even.
so, pick one even number from the first set. probability is 2/5
pick one even number from the second set. probability is 2/4
So, combined probability is 2/5 * 2/4 = 1/5.
What is the OA? |
the product is even if one of the two numbers is even or if both are even. You have considered the possibility that both are even and not accounted for the other two possibilities.
You can alternatively solve this question by finding out the probability of the event that is complementary to the one asked and subtract that probability from 1.
In this case, the complementary event is to find the probability that the product is odd.
The product will be odd, when the two numbers are both odd numbers.
The probability of getting an odd number from the 1st set = 3/5
The probability of getting an odd number from the 2nd set = 1/2
Therefore, the probability of getting an odd product = 3/5 * 1/2 = 3/10
Hence, the probability of getting the product that is even = 1 - 3/10 = 7/10
Choice (e) |
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