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GMATT73
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Nakib takes the GMAT twice, once on December 31 after a big 12 Dec 2005, 07:29
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100% (02:34) correct 0% (00:00) wrong based on 1 sessions

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Nakib takes the GMAT twice, once on December 31 after a big party, and once on January 2 after he is sober. If he has a 20% chance of scoring an 800 on 12/30 and a 30% chance of scoring an 800 on 1/2, What is the probability that he will get an 800 on either day?

A. 6%
B. 14%
C. 28%
D. 38%
E. 50%



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Nakib takes the GMAT twice, once on December 31 after a big 12 Dec 2005, 07:45
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GMATT73
Nakib takes the GMAT twice, once on December 31 after a big party, and once on January 2 after he is sober. If he has a 20% chance of scoring an 800 on 12/30 and a 30% chance of scoring an 800 on 1/2, What is the probability that he will get an 800 on either day?

A. 6%
B. 14%
C. 28%
D. 38%
E. 50%
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In real life.. it should be 0% (impossible).

:-D
now let's see this 2 events are munually exclusive that means both happening at the same time is impossible.

for mutually exclusive events, probability of A or B is simply P(A) + P(B)

so the answer is 20% + 30% = 50%

So E is the answer.
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Nakib takes the GMAT twice, once on December 31 after a big 12 Dec 2005, 08:09
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D

Dec30 = 2/10 , Jan2 = 3/10
Getting 800 on either day

2/10*7/10+3/10*8/10= 38/100= 38 %
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GMATT73
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cool_jonny009
D

Dec30 = 2/10 , Jan2 = 3/10
Getting 800 on either day

2/10*7/10+3/10*8/10= 38/100= 38 %
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Cool Johnny is definately coool :P

OA is (D)
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Yurik79
cool_jonny009
D

Dec30 = 2/10 , Jan2 = 3/10
Getting 800 on either day

2/10*7/10+3/10*8/10= 38/100= 38 %
Please explain what is 7/10 and 8/10?
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7/10 = Probability of Nabik not Getting 800 on Jan 2
8/10 = Probability of Nabik not Getting 800 on Dec 30

Getting 800 on either Day =
(Prob of 800 on Dec2) *(Prob of NOT 800 on JAN 2) + (Prob of 800 on JAN 2)*(Prob of NOT 800 on Dec2)
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Nakib takes the GMAT twice, once on December 31 after a big 12 Dec 2005, 10:17
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I get 44% (or 11/25) which is not in the ACs :P

the way I know nabik77, he won't worry about taking gmat again on 01/02 if he already got perfect 800 on 12/31

so the probability for getting 800 =
800 on 12/31 + (miss on 12/31) * 800 on 01/02 =
1/5 + 4/5 * 3/10 = 11/25 = ~44%
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Nakib takes the GMAT twice, once on December 31 after a big 12 Dec 2005, 10:21
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I guess all the answer choices are wrong.

It should be around 70%~80%, but none of the answer choices are above 50%.
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skif
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Nakib takes the GMAT twice, once on December 31 after a big 13 Dec 2005, 03:40
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duttsit
I get 44% (or 11/25) which is not in the ACs :P

the way I know nabik77, he won't worry about taking gmat again on 01/02 if he already got perfect 800 on 12/31

so the probability for getting 800 =
800 on 12/31 + (miss on 12/31) * 800 on 01/02 =
1/5 + 4/5 * 3/10 = 11/25 = ~44%
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Duttsit, You have got the probability to get 800 in one day + get 800 in both days.
Look
to get 800 at LEAST 1 time
P=1-0,7*0,8=0,44 (NOT lose 2 times)
to get 800 2 time
P=0,3*0,2=0,06
To get 800 ONLY 1 time P=0,44-0,06=0,38
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skif
duttsit
I get 44% (or 11/25) which is not in the ACs :P

the way I know nabik77, he won't worry about taking gmat again on 01/02 if he already got perfect 800 on 12/31

so the probability for getting 800 =
800 on 12/31 + (miss on 12/31) * 800 on 01/02 =
1/5 + 4/5 * 3/10 = 11/25 = ~44%

Duttsit, You have got the probability to get 800 in one day + get 800 in both days.
Look
to get 800 at LEAST 1 time
P=1-0,7*0,8=0,44 (NOT lose 2 times)
to get 800 2 time
P=0,3*0,2=0,06
To get 800 ONLY 1 time P=0,44-0,06=0,38
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Agree. As two events are NOT mutually exclusive:

p(800 on 1st attempt OR 800 on 2nd attempt) = p(800 on 1st) + p(800 on 2nd) - p(800 on both)
= 0.44 - 0.06 = 0.36

thanks skif for pointing that out.



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