GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 19 Oct 2019, 15:59

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Principal of a school recorded the number of students in each of 15 cl

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 58445
Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 02:22
00:00

Difficulty:

25% (medium)

Question Stats:

67% (00:37) correct 33% (01:11) wrong based on 65 sessions

### HideShow timer Statistics

Principal of a school recorded the number of students in each of 15 classes. What was the standard deviation of the numbers of students in the 15 classes?

(1) The average (arithmetic mean) number of students for all the classes was 30.
(2) Each classes had the same number of students.

_________________
examPAL Representative
Joined: 07 Dec 2017
Posts: 1153
Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 04:18

This question is resolved using the logic of standard deviation - SD is a measure of how spread out an average is. To find it, we need info about the variance of the values being checked, or the values themselves (the number of students in each class). Without that information, finding standard deviation is impossible.
_________________
e-GMAT Representative
Joined: 04 Jan 2015
Posts: 3074
Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 06:34

Solution

Given:
• The total number of classes = 15

To find:
• The standard deviation of the number of students in the 15 classes

Analysing Statement 1
• Given that the average number of students for all the classes = 30

But, we do not have any information about the number of students in each class.

Therefore, Statement 1 alone is not sufficient to answer this question.

Analysing Statement 2
• Given that each class had the same number of students
o Thus, deviation = 0

Therefore, Statement 2 alone is sufficient to answer this question

Hence, the correct answer is Option B

_________________
Intern
Joined: 24 Oct 2018
Posts: 10
Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 07:33
The standard deviation of the number of students in the 15 classes

Given that the average number of students for all the classes = 30

But, we do not have any information about the number of students in each class.

Therefore, Statement 1 alone is not sufficient to answer this question.

Therefore, Statement 2 alone is sufficient to answer this question
Option B
Intern
Joined: 25 Jul 2018
Posts: 11
Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 08:01
Q: std. deviation between # students in 15 classes

S1: avg
S2: each class same # students

S1: insufficient --> average is not enough to determine std. Says nothing about dispersion.

S2: each class same # students --> so difference of them from median 0 , # students class A = # students each other class = avg. the same too , so data points do not deviate from mean = Standard deviation 0

Hence, B imo.
Intern
Joined: 21 Apr 2018
Posts: 13
Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

### Show Tags

25 Oct 2018, 15:14
If the number of students in each class is the same; there is no deviation between the classes. In other words, zero deviation.

Re: Principal of a school recorded the number of students in each of 15 cl   [#permalink] 25 Oct 2018, 15:14
Display posts from previous: Sort by