Probability

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Probability

by Abdulla » Sun Jul 12, 2009 7:40 pm

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A certain school has 50 students assigned randomly to 5 distinct classes, and each student is assigned to only one class. If the numbers of students in the classes are consecutive, what is the probability that a given student is in one of the two largest classes?

(A) 48%
(B) 46%
(C) 42%
(E) 38%
(D) 34%
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by yogami » Sun Jul 12, 2009 8:30 pm
Well, first of all it says that 50 students are randomly distributed in the class and no student takes two classes. So this makes our lives easier (will not involve the whole set theory drama). Secondly it also says that number of students are consecutive over the classes. So only one consecutive sequence fits the breakdown (8,9,10,11,12). Now the odds of picking a student from the two largest classes i,e from the classes with counts 11 and 12 are (11 + 12)/50
so 23/50 which is 46%
200 or 800. It don't matter no more.

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Concur

by uw490 » Mon Jul 13, 2009 1:07 pm
Agreed. I also got 46%, B...

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by Scott@TargetTestPrep » Sun May 19, 2019 6:30 pm
Abdulla wrote:A certain school has 50 students assigned randomly to 5 distinct classes, and each student is assigned to only one class. If the numbers of students in the classes are consecutive, what is the probability that a given student is in one of the two largest classes?

(A) 48%
(B) 46%
(C) 42%
(E) 38%
(D) 34%
Since the average number of students per class is 50/5 = 10 and the the number of students in the 5 classes are consecutive numbers, then the number of students in the 5 classes are 8, 9, 10, 11 and 12. Thus, the probability that a given student is in one of the two largest classes is:

(11 + 12)/50 = 23/50 = 46/100 = 46%

Answer: B

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