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

Redeem

Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

★★★★★5.0559 reviews
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

Standard Deviation Problem

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 23
Joined: Mon Jan 07, 2008 12:55 pm
Location: Frisco, Texas
by adi » Sat Mar 08, 2008 2:28 pm
For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

A) 74
B) 76
C) 78
D) 80
E) 82

The correct answer should be A.

Thanks in advance! :D
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members
Location: Toronto
Thanked: 1710 times
GMAT Score:800

Re: Standard Deviation Problem

by Stuart@KaplanGMAT » Sat Mar 08, 2008 3:36 pm
adi wrote:For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

A) 74
B) 76
C) 78
D) 80
E) 82

The correct answer should be A.

Thanks in advance! :D
We can set up two equations with two unknowns to solve this problem.

Let M = the mean
Let SD = 1 standard deviation

M + 3SD = 98
M - 2SD = 58

if we subtract we get:

5SD = 40
SD = 8

and subbing back in:

M - 2(8) = 58
M = 58 + 16
M = 74

We also could have used logic rather than equations:

The spread between 58 and 98 is a total of 5 standard deviations (one is 2 below, one is 3 above), so those 5 SDs = 40, and 1 SD = 40/5 = 8.

If 58 is 2 SDs below the mean, then 58 + 2(8) = 74 is the mean.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 39
Joined: Sun Apr 13, 2008 12:17 am

by yalephd2007 » Sun Apr 13, 2008 4:56 pm
thank you for your detailed explonation
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 36
Joined: Tue Oct 02, 2007 10:25 am
Thanked: 2 times

by dalwow » Wed Apr 16, 2008 12:13 pm
Stuart-

For this problem I just took the total variance (98-58 ) which was 40 and divided that by 5 standard deviations. That told me one standard deviation was 8 pts. Then we could easily figure it out from that. Is that just a coincidence for this problem or is that a viable way to work this out in the future? Thanks

Chris
Still Learning
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Fri Sep 26, 2008 7:21 am
Thanked: 1 times

by Natalllllia » Mon Dec 01, 2008 8:30 pm
thank you
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 1462
Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members
Location: New York, NY
Thanked: 39 times

by Jeff@TargetTestPrep » Thu Aug 30, 2018 4:46 pm
adi wrote:For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

A) 74
B) 76
C) 78
D) 80
E) 82
If we let x = mean and s = standard deviation, then a score of 58 that was 2 standard deviations below the mean would mean 58 = x - 2s. Similarly, a score of 98 that was 3 standard deviations above the mean would mean 98 = x + 3s.

We can use the two equations to determine a value of x.

x - 2s = 58

x + 3s = 98

If we subtract the first equation from the second equation, we have:

5s = 40

s = 8

Now we can determine x:

x + 3s = 98

x + 3(8) = 98

x + 24 = 98

x = 74

Answer: A

Jeffrey Miller
Head of GMAT Instruction
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Mon Sep 03, 2018 7:52 pm
Hi All,

We're told that for a certain examination, a score of 58 was 2 standard deviations BELOW the mean and a score of 98 was 3 standard deviations ABOVE the mean. We're asked for the mean score for the examination. The math behind this question is just basic Algebra, but depending on how you organize your information, you can save some time on the math that you'll need to do.

To start, the difference between a 98 and a 58 is 5 total Standard Deviations (since a 98 is '3 above' and a 58 is '2 below'). Thus, 98 - 58 = 40 is equal to 5 Standard Deviations.
40/5 = 8... meaning that 1 Standard Deviation is 8 'away' from the mean. At this point, we can either "go up" from 58 or "go down" from 98, but we'll get to the Mean either way as long as we're counting up the proper number of Standard Deviations.

From 58, we add 2 S.D.s --> 58 + 2(8) = 74
From 98, we subtract 3 S.D.s --> 98 - 3(8) = 74

Final Answer: A

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1