In such questions always remember mean is the mid point which means 50% values is greater than the mean and 50% are below the mean
Mean = m
SD=d
Always remember the 68-95-99.8 rule of statistics
Here is a link which will help you understand this rule
https://en.wikipedia.org/wiki/68-95-99.7_rule
Mean + 1stSD = m+d - 34%
Mean + 2ndSD = m+2d - 14%
Mean + 3rdSD = m+3d - 2%
similarly for below the mean
Mean - 1stSD = m-d - 34%
Mean - 2ndSD = m-2d - 14%
Mean - 3rdSD = m-3d - 2%
Statement I
68% of the values lies within m+d and m-d
This mean 34% of values lies within the 1st SD above the mean and 34% lies within 1st SD below the mean.
We have to find the percentage greater then 1st SD above the mean
50%-34% = 16%
Therefore sufficient.
Statement II
16% of the values are less than m-d
Therefore 16% of the values would be more than m+d.
Therefore sufficient.
Hence D is the answer.
Let me know if you have any doubts.
BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course
Redeem
Featured Course
Target Test Prep GMAT OnDemand
Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.
- 715+ score guarantee — highest in the industry (99th percentile)
- 52 chapters · 1,500+ lessons · 4,000+ practice questions
- 400 hours of video · 1,500+ instructor-led HD smartboard lessons
- 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
- 24/7 live support + weekly Zoom office hours with GMAT instructors
- TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
- 1,200+ flashcards + AI-powered study assistant & daily calendar
- OnDemand, LiveTeach & GMAT Bootcamp formats available
- Also: GRE, SAT Math & Executive Assessment courses
- MBA Admissions Consulting now available
- 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
- 200,000+ students served
- 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★
5.0
(559 reviews)
130-pt guarantee
$0 to start
then $127/mo
another DS
Source: Beat The GMAT — Data Sufficiency |
GMAT/MBA Expert
-
Ian Stewart
- GMAT Instructor
- Posts: 2623
- Location: Montreal
- Thanked: 1090 times
- GMAT Score:780
This is true in this question, because you know the distribution is symmetric. When a distribution is symmetric, the median and the mean are equal. However, in many sets you'll encounter on the GMAT, the median and the mean will be different.parallel_chase wrote:In such questions always remember mean is the mid point which means 50% values is greater than the mean and 50% are below the mean
This rule only applies to data that is 'normally distributed', something which you can never assume to be the case on the GMAT (and you don't need to know what 'normally distributed' means, either). The 68-95-99.7 rule is not true for arbitrary distributions of data, nor is it tested on the GMAT. You don't need to know anything about normal distributions to solve the above problem, and you don't need the 68-95-99.7 rule; you only need to know what is meant by 'symmetric distribution'.parallel_chase wrote:
Always remember the 68-95-99.8 rule of statistics
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com
ianstewartgmat.com
ianstewartgmat.com
