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Probability

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Probability

by umaa » Thu Jul 17, 2008 9:00 pm
GMAT- Quantitative Section: A{1,2,3,4} and B{5,6,7,8}. I randomly select an integer from A and from B. What’s the probability that my two integers add up to 8?

A. 0.625

B. 0.125

C. 0.25

D. 0.1875

E. 0.75


Answer: D
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by reachac » Thu Jul 17, 2008 9:31 pm
Ok possible arrangements to suffice the given condition are.

[1,7], [2,6] and [3,5]

each of the above has a probability of [1/4]*[1/4]= 1/16

so total probabilty for the 3 is 3/16
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by umaa » Thu Jul 17, 2008 10:39 pm
I'm dumb in probability. Can you explain me how 1/4 * 1/4 came?

thx.
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by sudhir3127 » Thu Jul 17, 2008 10:45 pm
probability of chossing two number from 8 is 2/8 = 1/4

i did in this way for the sum to be 8 the numbers are

(1,7) ,(2,6) and (3,5) so its 3 favourable occurences

total number of occurences is 4*4=16

hence the probability is 3/16.

hope it helps..
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