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Defective roll probability

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by jcnissi » Thu Nov 18, 2010 8:34 pm
There are 15 rolls of film in a box and 3 are defective. Two rolls are to be selected, one after the other. What is the probability of selecting a defective roll followed by another defective roll?
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by Rahul@gurome » Thu Nov 18, 2010 9:25 pm
jcnissi wrote:There are 15 rolls of film in a box and 3 are defective. Two rolls are to be selected, one after the other. What is the probability of selecting a defective roll followed by another defective roll?
Defective number of rolls = 3
Total number of rolls = 15
Probability of selecting a defective roll out of 15 = 3/15

Now, Defective number of rolls = 2
Total number of rolls = 14
Probability of selecting a defective roll out of 14 = 2/14

Required probability = (3/15)*(2/14) = 1/35
Last edited by Rahul@gurome on Fri Nov 19, 2010 5:03 am, edited 1 time in total.
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by hoji » Fri Nov 19, 2010 4:45 am
Rahul, i think 3 are defective of those 15 rolls, so my solution is:
probability of coming the first roll out as a defective is 3/15 and consequently the second one`s is 2/14 and taking them together, it is like 3/15*2/14=1/35
what do you say?
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by Rahul@gurome » Fri Nov 19, 2010 5:04 am
hoji wrote:Rahul, i think 3 are defective of those 15 rolls, so my solution is:
probability of coming the first roll out as a defective is 3/15 and consequently the second one`s is 2/14 and taking them together, it is like 3/15*2/14=1/35
what do you say?
Thanks hoji!
Edited the reply. :)
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