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

Redeem

GMATPrep Mean and standard deviation...Pls pls pls help.....

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Wed Aug 17, 2011 4:14 am

GMATPrep Mean and standard deviation...Pls pls pls help.....

by saisree » Thu Nov 03, 2011 6:03 am
A list of numbers is as shown below

70, 75, 80, 85, 90, 105, 105, 130, 130, 130

It shows the times in seconds which it took for each of 10 school children to run a distance of 400kilometers. If the standard deviation of the 10 running times is 22.4, how many running times are more than 1 standard deviation below the mean of the 10 running times?

a) One
b) Two
c) Three
d) Four
e) Five

Pls pls pls help. Thanks in advance.
Top
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 349
Joined: Wed Sep 28, 2011 3:38 pm
Location: Austin, TX
Thanked: 236 times
Followed by:54 members
GMAT Score:770

by GmatMathPro » Thu Nov 03, 2011 6:32 am
First, calculate the average: The total of the times is 1000, so the average is 100. One standard deviation BELOW the mean would then be 100-22.4=77.6. How many times are below 77.6? Just two: 70, and 75.

Ans: B
Pete Ackley
GMAT Math Pro
Free Online Tutoring Trial
Top
User avatar
Community Manager
Posts: 1060
Joined: Fri May 13, 2011 6:46 am
Location: Utrecht, The Netherlands
Thanked: 318 times
Followed by:52 members

by neelgandham » Thu Nov 03, 2011 6:37 am
The total of the times is 1000, i.e average is 100.

Standard Deviation = 22.4

Question: running times are more than 1 standard deviation below the mean. i.e How many times are below 100-22.4? (70, and 75).

IMO : B
Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Top
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Wed Aug 17, 2011 4:14 am

by saisree » Thu Nov 03, 2011 6:55 am
Thank you so much. OA is B.
Top
Post new topic Post Reply
• Page 1 of 1