probability

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probability

by Ramit88 » Tue Jan 25, 2011 10:13 pm
A = {2, 3, 4, 5}
b = {4, 5, 6, 7, 8}

Two integers will be randomly selected from the sets above, one from set A and one from set B. What is the prob that the sum of two integers will equal 9 ?

A 0.15
B 0.20
C 0.25
d 0.30
E 0.33


ANS B

am getting B
my approach
total possible sets of two no. = 4X5= 20

totals sets when sum is 9 = (2,7) (3,6) (4,5)

prob = 3/20
= 0.15

pls point out my mistake
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by Anurag@Gurome » Tue Jan 25, 2011 10:37 pm
Ramit88 wrote:my approach
total possible sets of two no. = 4X5= 20

totals sets when sum is 9 = (2,7) (3,6) (4,5)

prob = 3/20
= 0.15

pls point out my mistake
You're missing one possible set : 5 from set A and 4 from set B.
Hence, total number of favorable cases = 4

Required probability = 4/20 = 1/5 = 0.20

The correct answer is B.
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by Ramit88 » Tue Jan 25, 2011 11:57 pm
Anurag@Gurome wrote:
Ramit88 wrote:my approach
total possible sets of two no. = 4X5= 20

totals sets when sum is 9 = (2,7) (3,6) (4,5)

prob = 3/20
= 0.15

pls point out my mistake
You're missing one possible set : 5 from set A and 4 from set B.
Hence, total number of favorable cases = 4

Required probability = 4/20 = 1/5 = 0.20

The correct answer is B.


isnt the set (4,5) and (5,4) same??

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by Anurag@Gurome » Tue Jan 25, 2011 11:59 pm
Ramit88 wrote:isnt the set (4,5) and (5,4) same??
No.
In the 1st case, i.e. (4, 5) : 4 is from set A and 5 is from set B
In the 2nd case, i.e. (5, 4) : 5 is from set A and 4 is from set B
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by Ramit88 » Wed Jan 26, 2011 12:13 am
thanks anurag...u r awesome