Probability

Expert replies

Abdulla: Master | Next Rank: 500 Posts; Posts: 328; Joined: Thu Aug 07, 2008 5:25 pm; Location: Philadelphia; Thanked: 4 times; GMAT Score:550

by Abdulla » Sun Jul 12, 2009 7:40 pm

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%

Abdulla

Like this post

Source: Beat The GMAT — Problem Solving | Sun Jul 12, 2009 7:40 pm

yogami: Master | Next Rank: 500 Posts; Posts: 170; Joined: Tue May 26, 2009 12:00 pm; Thanked: 5 times

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.

Like this post

uw490: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Sat May 02, 2009 7:24 pm

Concur

by uw490 » Mon Jul 13, 2009 1:07 pm

Agreed. I also got 46%, B...

Like this post

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8154; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

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

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review