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How to solve this Q?

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by sanaa.rizwan » Mon Apr 08, 2013 4:35 pm
NP: OG PS 68

A={2,3,4,5}
B={4,5,6,7,8}

Two integers will be randomly selected from the sets above. One from A and one from B. what is the probability that the sum of the two integers will equal 9

A. 0.15
B. 0.20
C. 0.25
D. 0.30
E. 0.33
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Source: — Problem Solving |

by GMATGuruNY » Mon Apr 08, 2013 4:46 pm
sanaa.rizwan wrote:NP: OG PS 68

A={2,3,4,5}
B={4,5,6,7,8}

Two integers will be randomly selected from the sets above. One from A and one from B. what is the probability that the sum of the two integers will equal 9

A. 0.15
B. 0.20
C. 0.25
D. 0.30
E. 0.33
P = (good outcomes)/(total possible outcomes).

Total possible outcomes:
Number of options from set A = 4.
Number of options from set B = 5.
To combine these options, we multiply:
4*5 = 20.

Good outcomes:
A good outcome occurs when A+B = 9:
A=2 and B=7.
A=3 and B=6.
A=4 and B=5.
A=5 and B=4.
Total options = 4.

(Good options)/(total possible options) = 4/20 = .2.

The correct answer is B.
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