Probability

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

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

Probability

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

Quote

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.

Quote

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...

Quote

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

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]