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

Redeem

Beat the Stats PS

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 258
Joined: Fri Jun 22, 2012 4:39 am
Location: Bengaluru, India
Thanked: 6 times
Followed by:3 members
GMAT Score:640

Beat the Stats PS

by sachindia » Fri Jan 04, 2013 5:53 am
70 75 80 85 90 105 105 130 130 130

The list shown consist of the times,in seconds, that it took each of 10 school children to run a distance of 400 meter. If the SD of ten running times is 22.4 seconds,rounded to nearest tenth of second,how many of the 10 running times are more than one SD below the mean of the 10 running times?

a. one
b. two
c. three
d. four
e. five

[spoiler]Ans : B[/spoiler]
Regards,
Sach
Top
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 65
Joined: Wed Mar 28, 2012 6:54 pm
Location: Canada
Thanked: 15 times
Followed by:1 members

by Param800 » Fri Jan 04, 2013 6:33 am
(1) First calculate the mean of all the data given...which comes out to be 100

(2) Now, the standard deviation is 22.4, so one standard deviation below the mean would be 100-22.4 = 77.6.

(3)Now, we have to calculate the value corresponding with one standard deviation below the mean. We check the data points and find the points which are below 77.6. Only such points are 70 and 75

Thus, answer is 2 (B)

Hope this helps
Top
Master | Next Rank: 500 Posts
Posts: 258
Joined: Fri Jun 22, 2012 4:39 am
Location: Bengaluru, India
Thanked: 6 times
Followed by:3 members
GMAT Score:640

by sachindia » Fri Jan 04, 2013 6:50 am
but question is .. how many of the 10 running times are more than one SD below the mean of the 10 running times?

so it shud be 8, right?
Regards,
Sach
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Fri Jan 04, 2013 7:14 am
sachindia wrote:but question is .. how many of the 10 running times are more than one SD below the mean of the 10 running times?

so it shud be 8, right?
The key word here is "below," which can be interpreted as "less than."
Similar sentence: "The sale price is more than $20 below the regular price."

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Master | Next Rank: 500 Posts
Posts: 258
Joined: Fri Jun 22, 2012 4:39 am
Location: Bengaluru, India
Thanked: 6 times
Followed by:3 members
GMAT Score:640

by sachindia » Fri Jan 04, 2013 8:11 am
Thanks Brent.. I get it now..
It is asking for the distribution points that lie in the region less than |m-d|

distribution usually is like below:

m-2d m-d d m+d m+2d ..

Please correct me if anything is wrong..
Regards,
Sach
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Fri Jan 04, 2013 8:21 am
sachindia wrote:Thanks Brent.. I get it now..
It is asking for the distribution points that lie in the region less than |m-d|

distribution usually is like below:

m-2d m-d d m+d m+2d ..

Please correct me if anything is wrong..
Yes, that seems correct (I'm assuming that d = standard deviation)

Aside: we don't really need the absolute value (as in "|m-d|")

I'd say that we're looking for the distribution points that lie in the region less than m-d

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Post new topic Post Reply
• Page 1 of 1