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# Probability_independent

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Director
Joined: 22 Aug 2007
Posts: 572
Followers: 1

Kudos [?]: 14 [0], given: 0

Probability_independent [#permalink]  03 Sep 2007, 00:21
DS
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GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5079
Location: Singapore
Followers: 21

Kudos [?]: 180 [0], given: 0

St1:
P(A) = 0.25. But we do not know P(B). Insufficient.

St2:
P(!B) = 0.71. But we do not know anything about P(A). Insufficient.

Using both, we know P(A) = 0.25, P(B) = 1-0.71 = 0.29. So we can calculate P(A) * P(B) and determine if it is greater than 0.3.

Ans C
Intern
Joined: 05 Apr 2007
Posts: 11
Followers: 0

Kudos [?]: 2 [0], given: 0

Probability P(A and B) for independen events A and B is P(A).P(B)

1st condition.... P(A) = 0.25.
Since P(B) <1 so P(A).P(B) <0.3 SUFFICIENT

2nd condition .... P(B) = 1-0.71 = 0.29
Since P(A) <1 so P(A).P(B) < 0.3 SUFFICIENT

So each alone is sufficient. (D) is correct.
Manager
Joined: 03 Sep 2006
Posts: 233
Followers: 1

Kudos [?]: 5 [0], given: 0

I got into trap and answered C (the same method as ywilfred)

zzyyxx: Thanks a lot!
Director
Joined: 22 Aug 2007
Posts: 572
Followers: 1

Kudos [?]: 14 [0], given: 0

zzyyxx wrote:
Probability P(A and B) for independen events A and B is P(A).P(B)

1st condition.... P(A) = 0.25.
Since P(B) <1 so P(A).P(B) <0.3 SUFFICIENT

2nd condition .... P(B) = 1-0.71 = 0.29
Since P(A) <1 so P(A).P(B) < 0.3 SUFFICIENT

So each alone is sufficient. (D) is correct.

Thanks! that question is tricky
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