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Probability and combinations

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by venmic » Sat Aug 07, 2010 8:20 am
Denise is trying to open a safe whose combination she does not know If the safe has 4000 possible combinations and she can try 75 different possibilities what is the probability that she does not pick the one correct combination

1
159/160
157/160
3/160
0

Do not know answer
This is a Kaplan question
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by kvcpk » Sat Aug 07, 2010 8:28 am
venmic wrote:Denise is trying to open a safe whose combination she does not know If the safe has 4000 possible combinations and she can try 75 different possibilities what is the probability that she does not pick the one correct combination

1
159/160
157/160
3/160
0

Do not know answer
This is a Kaplan question
Buddy.. Can you post this in the right forum? - Problem Solving.
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by thephoenix » Sat Aug 07, 2010 8:37 am
moderators please transfer the question in right forum

ans should be c

probability of getting a correct combination is 75/4000=3/160
P of not getting any correct combination is 1-3/160=157/160
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by venmic » Sat Aug 07, 2010 9:49 am
sorry about that

but the last post came as

probability of getting a correct combination is 75/4000=3/160

can you plaease explain the concept of a 75/4000
I mean the logic behind it

Thanks for ur help
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by kvcpk » Sat Aug 07, 2010 10:23 am
venmic wrote:sorry about that

but the last post came as

probability of getting a correct combination is 75/4000=3/160

can you plaease explain the concept of a 75/4000
I mean the logic behind it

Thanks for ur help
Probability of good outcomes = (Number of good outcomes)/ Total Outcomes
Number of good outcomes here are 75
Total number of outcomes = 4000
Hence probability = 75/4000

Now we require bad outcomes probability. hence subtract the result from 1
1= 75/4000 = 157/160

Hope this helps!!
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by thephoenix » Sat Aug 07, 2010 10:29 am
venmic wrote:sorry about that

but the last post came as

probability of getting a correct combination is 75/4000=3/160

can you plaease explain the concept of a 75/4000
I mean the logic behind it

Thanks for ur help
there is only one combination for opening the safe out of 4000
now Denise is trying 75 combination
now if the combination exists in these 75 trials then denise can do it in 75C1 ways=75
he can select one combination out of 4000 combination in 4000 ways
so probability of getting a correct combination is 75/4000

hth
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by venmic » Sat Aug 07, 2010 1:08 pm
Thankyou Sir
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by selfmade » Sun Aug 08, 2010 6:54 am
one more vote for 157/160. The explaination provided by thephoneix is really good.
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Aiming for 780
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