Author 
Message 
TAGS:

Hide Tags

Senior Manager
Joined: 07 Sep 2010
Posts: 288

Website W receives orders for its products every day. What
[#permalink]
Show Tags
08 Oct 2013, 09:01
Question Stats:
69% (00:31) correct 31% (00:31) wrong based on 808 sessions
HideShow timer Statistics
Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days? (1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days. (2) The range of the number of orders that Website W received daily for the past 5 days is Zero.
Official Answer and Stats are available only to registered users. Register/ Login.




Math Expert
Joined: 02 Sep 2009
Posts: 47871

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
09 Oct 2013, 00:59
Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days?(1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days. Since mean=greatest, then the number of orders each day was the same. This implies that the standard deviation is 0 (the standard deviation of a set is zero if and only the set consists of identical numbers). Sufficient. (2) The range of the number of orders that Website W received daily for the past 5 days is Zero. Basically the same here: since the range is 0 (greatestsmallest=0 > greatest=smallest), then the number of orders each day was the same. Sufficient. Answer: D.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Manager
Joined: 18 Dec 2012
Posts: 97
Location: India
Concentration: General Management, Strategy
GMAT 1: 660 Q49 V32 GMAT 2: 530 Q37 V25
GPA: 3.32
WE: Manufacturing and Production (Manufacturing)

Re: Website W receives order
[#permalink]
Show Tags
08 Oct 2013, 09:20
imhimanshu wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days? a) The Average(Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days. b) The range of the number of orders that Website W received daily for the past 5 days is Zero. Hi, Standard Deviation = Sum of the square of the variations from mean / total number of entities. Statement 1 : The average of number of orders = Greatest order of the day. Hence the variation = 0, so the SD = 0 Sufficient Statement 2 : Range = Max value  min value Here the range = 0 The number of orders = 0 ( Number of orders can't be negative) So SD = 0 Sufficient Both the statements are sufficient Option D Hope it is clear Cheers Qoofi
_________________
I'm telling this because you don't get it. You think you get it which is not the same as actually getting it. Get it?



Manager
Joined: 29 Aug 2013
Posts: 74
Location: United States
Concentration: Finance, International Business
GMAT 1: 590 Q41 V29 GMAT 2: 540 Q44 V20
GPA: 3.5
WE: Programming (Computer Software)

Re: Website W receives order
[#permalink]
Show Tags
09 Oct 2013, 00:51
imhimanshu wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days? a) The Average(Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days. b) The range of the number of orders that Website W received daily for the past 5 days is Zero. For standard deviation you just need to know if the numbers in the sequence are in some particular order. For eg in case of consecutive numbers the deviation can be calculated. and if all the numbers in a particular sequence are same then the deviation will be 0. Statement 1: If the average of the numbers is equal to the greatest of all the numbers then all the numbers have to be that greatest number. Hence there is no deviation. eg. 3,4,5 the greatest is 5 but average is 4. So it all the numbers have to be 5 for the average to be 5. But if it were stated that the median is equal to the highest then it would have been insufficient since median can be the greatest number of those 5 days and the first 2 can be different. hence Sufficient. Statement 2: If the range is 0, then the highest number of delivery  lowest number of delivery is 0. So if the highest number in the sequence is equal to the lowest number in the sequence, all the numbers in that sequence has to be same. hence Sufficient



Intern
Joined: 21 Oct 2012
Posts: 35
Location: United States
Concentration: Marketing, Operations
GMAT 1: 650 Q44 V35 GMAT 2: 600 Q47 V26 GMAT 3: 660 Q43 V38
GPA: 3.6
WE: Information Technology (Computer Software)

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
08 Dec 2014, 09:50
Bunuel wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days?
(1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days.
Since mean=greatest, then the number of orders each day was the same. This implies that the standard deviation is 0 (the standard deviation of a set is zero if and only the set consists of identical numbers). Sufficient.
(2) The range of the number of orders that Website W received daily for the past 5 days is Zero.
Basically the same here: since the range is 0 (greatestsmallest=0 > greatest=smallest), then the number of orders each day was the same. Sufficient.
Answer: D. Hi Bunuel, Can you please explain statement 1 with some kind of mathematical equation? I know it seems kind of silly of me but for the life of me i cant seem to wrap my head around it Thanks, Aamir.



Intern
Joined: 08 Oct 2015
Posts: 10

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
13 Oct 2015, 22:12
Out of curiosity, how do you guys know the difficulty range of these questions (i.e. 600700) or are these just guesses on the part of the thread originator?



Math Expert
Joined: 02 Sep 2009
Posts: 47871

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
18 Oct 2015, 13:42



Intern
Joined: 06 Mar 2015
Posts: 3

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
13 May 2016, 22:28
Hi Bunuel,
Thanks for your crystal clear explanation. However, i have a question. If the first option is written as :'The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the least of the number of orders that Website W received daily for the past 5 days', what would be the answer. I believe it would be insufficient to answer using the first option. Please comment.
Thanks, Khitindra



Math Expert
Joined: 02 Aug 2009
Posts: 6499

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
13 May 2016, 22:33
khitindra wrote: Hi Bunuel,
Thanks for your crystal clear explanation. However, i have a question. If the first option is written as :'The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the least of the number of orders that Website W received daily for the past 5 days', what would be the answer. I believe it would be insufficient to answer using the first option. Please comment.
Thanks, Khitindra Hi khitindra, If the sentence was :'The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the least of the number of orders that Website W received daily for the past 5 days since average = least, this means all the orders are same .... average can be equal to least or greatest ONLY when the orders are same... say least and average are 10, so if any orders above this would change the average so all have to be SAME
_________________
1) Absolute modulus : http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html 3) effects of arithmetic operations : https://gmatclub.com/forum/effectsofarithmeticoperationsonfractions269413.html
GMAT online Tutor



Senior SC Moderator
Joined: 14 Nov 2016
Posts: 1322
Location: Malaysia

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
18 May 2017, 18:03
imhimanshu wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days?
(1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days.
(2) The range of the number of orders that Website W received daily for the past 5 days is Zero. Each statement says the same thing. Range = 0. If the mean = the max, then all the numbers are the same. Try some sets of numbers to see, that will help on test day. Say the mean is 5 and the max is 5 OK, then if I have any other number in the set. Say 4, {4, 5}, mean isn't 5 any more, too small So all the numbers = 5 Answer : D
_________________
"Be challenged at EVERY MOMENT."
“Strength doesn’t come from what you can do. It comes from overcoming the things you once thought you couldn’t.”
"Each stage of the journey is crucial to attaining new heights of knowledge."
Rules for posting in verbal forum  Please DO NOT post short answer in your post!
Advanced Search : https://gmatclub.com/forum/advancedsearch/



Intern
Joined: 13 Jul 2017
Posts: 3

Website W receives orders for its products every day. What
[#permalink]
Show Tags
25 Jul 2017, 09:22
Another approach to solve this.
(1) Let's say: a<b<c<d<e Average is equal to the greatest: (a+b+c+d+e)/5=e > a+b+c+d+e=5e > a+b+c+d = 4e All elements are equal. Standard deviation is 0. Sufficient.
(2) If the range is 0 it means that all elements are equal, like in (1). So, sufficient too.
Answer: D.



Director
Joined: 12 Nov 2016
Posts: 772
Location: United States
GPA: 2.66

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
10 Sep 2017, 22:02
imhimanshu wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days?
(1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days.
(2) The range of the number of orders that Website W received daily for the past 5 days is Zero. Housekeeping tipsIf the min or max equals the mean(average) then the standard deviation is 0 If the range of the set is zero this means the standard deviation is 0 St 1 follows rule 1 suff St 2 follows rule 2 suff D



Intern
Joined: 09 Oct 2016
Posts: 35

Re: Please help why the below DS problem results in D as the correct answe
[#permalink]
Show Tags
13 Oct 2017, 21:31
sophieyu0717 wrote: Web site W receives orders for its products every day. What is the standard deviation of the numbers of orders that Web Site W received daily for the past 5 days?
(1) The average (arithmetic mean) number of orders that Web Site W received per day for the past 5 days is equal to the greatest of the numbers of orders that Web Site W received daily for the past 5 days.
(2) The range of the numbers of orders that Web Site W received daily for the past 5 days is equal to 0. First, you need to understand the meaning of standard deviation. Standard deviation measures how far a certain point is from the mean. For example, let's consider the following data : (1, 2, 3, 4, 5). The the mean of these data equal (1+2+3+4+5)/5 =15/5 = 3. Now, you can see that the largest point 5 and 1 are two points from the mean. 2 and 4 are 1 point from the mean. 3 is zero point from the mean. The range of our example is equal to the large value minus the smallest value (51=4) Now, let's go back to the main question. 1 telling you that the mean is equal to the greatest number in the set ( for example if the mean is 5 then the greatest and also the smallest numbers are 5 too . This means that all of the five days have the same number of orders thus each day is 0 point from the mean. This is sufficient. 2 is talking about the range. It's telling you that the largest number is equal the smallest number. This means that all of the numbers in the five years are equal, thus each and each day is zero point from the mean. This is sufficient too.



Intern
Joined: 29 Sep 2015
Posts: 7

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
30 Oct 2017, 04:14
Hi Bunuel, any similar questions one could practice?



Math Expert
Joined: 02 Sep 2009
Posts: 47871

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
30 Oct 2017, 04:20



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 3150
Location: United States (CA)

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
03 Jan 2018, 11:07
imhimanshu wrote: Website W receives orders for its products every day. What is the Standard Deviation of the number of orders that Website W received daily for the past 5 days?
(1) The Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days is equal to the greatest of the number of orders that Website W received daily for the past 5 days.
(2) The range of the number of orders that Website W received daily for the past 5 days is Zero. We need to determine the standard deviation of the numbers of orders that website W received daily for the past 5 days. Statement One Alone: The average (arithmetic mean) number of orders that website W received per day for the past 5 days is equal to the greatest of the numbers of orders that website W received daily for the past 5 days. The only way for the average of the number of orders to be equal to the greatest number of orders is if all the values are the same. Thus, the standard deviation is 0. Statement one alone is sufficient to answer the question. Statement Two Alone: The range of the numbers of orders that Web site W received daily for the past 5 days is equal to 0. Since the range is equal to zero, all the numbers of the orders are the same, and thus the standard deviation is 0. Statement two alone is sufficient to answer the question. Answer: D
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Intern
Joined: 06 Oct 2016
Posts: 8

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
12 Jun 2018, 02:06
What key words tell us that the question asks for average per day and not between days? I thought it asked for average of 5 days. If that's the case, statement 2 could be insufficient as:
Day 1: 3,3,3 orders Day 2: 5,5,5 orders
Where range for each day could be 0 but SD between days could be anything. Thanks in advance.



DS Forum Moderator
Joined: 22 Aug 2013
Posts: 1337
Location: India

Re: Website W receives orders for its products every day. What
[#permalink]
Show Tags
12 Jun 2018, 22:35
Andy24 wrote: What key words tell us that the question asks for average per day and not between days? I thought it asked for average of 5 days. If that's the case, statement 2 could be insufficient as:
Day 1: 3,3,3 orders Day 2: 5,5,5 orders
Where range for each day could be 0 but SD between days could be anything. Thanks in advance. Hello First statement clearly says, " Average (Arithmetic Mean) number of orders that Website W received each per day for the past 5 days...". Second statement clearly says, " range of the number of orders that Website W received daily for the past 5 days..." And the question does NOT ask for average per day, the question asks for Standard Deviation for the 5 days. And your phrase 'average between days' is not clear.. can you please explain?




Re: Website W receives orders for its products every day. What &nbs
[#permalink]
12 Jun 2018, 22:35






