It is currently 12 Dec 2017, 14:08

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Let S be a finite set of consecutive multiples of 7.

Author Message
TAGS:

Hide Tags

Current Student
Joined: 23 Jul 2012
Posts: 37

Kudos [?]: 33 [3], given: 43

GPA: 3.9
Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

28 Jun 2013, 21:03
3
KUDOS
18
This post was
BOOKMARKED
00:00

Difficulty:

95% (hard)

Question Stats:

28% (01:13) correct 72% (01:30) wrong based on 225 sessions

HideShow timer Statistics

Let S be a finite set of consecutive multiples of 7. How many terms are there in S?

(1) The sum of the terms in set S is 105.
(2) The standard deviation of set S is equal to 3.5
[Reveal] Spoiler: OA

Kudos [?]: 33 [3], given: 43

Math Expert
Joined: 02 Sep 2009
Posts: 42571

Kudos [?]: 135384 [8], given: 12691

Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

28 Jun 2013, 21:43
8
KUDOS
Expert's post
10
This post was
BOOKMARKED
Let S be a finite set of consecutive multiples of 7. How many terms are there in S?

(1) The sum of the terms in set S is 105. Clearly insufficient. For example, consider S={28, 35, 42} and {49, 56}.

(2) The standard deviation of set S is equal to 3.5. Important property: if we add or subtract a constant to each term in a set SD will not change. From this it follows, that:

Any set with two consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7}, {7, 14}, {14, 21}, {21, 28}, ... will have the same standard deviation.
Any set with three consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14}, {7, 14, 21}, {14, 21, 28}, {21, 28, 35}, ... will have the same standard deviation.
Any set with four consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14, 21}, {7, 14, 21, 28}, {14, 21, 28, 35}, {21, 28, 35, 42}, ... will have the same standard deviation.
...

We know the standard deviation of S is 3.5. We CAN get the standard deviations of {0, 7}, {0, 7, 14}, {0, 7, 14, 21}, ... Only one of them will have the standard deviation of 3.5. So, we can get how many terms are there in the set. Sufficient.

Hope it's clear.
_________________

Kudos [?]: 135384 [8], given: 12691

Intern
Joined: 29 Oct 2013
Posts: 19

Kudos [?]: 14 [0], given: 8

Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

01 Sep 2014, 07:53
Can you post a link for tips on Standard Deviations? I'm a baby with S.D's! :/

Kudos [?]: 14 [0], given: 8

Math Expert
Joined: 02 Sep 2009
Posts: 42571

Kudos [?]: 135384 [0], given: 12691

Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

01 Sep 2014, 07:57
fra wrote:
Can you post a link for tips on Standard Deviations? I'm a baby with S.D's! :/

Theory on SD: math-standard-deviation-87905.html

Check Standard Deviation Questions in our Special Questions Directory.

Hope it helps.
_________________

Kudos [?]: 135384 [0], given: 12691

Current Student
Joined: 28 Nov 2014
Posts: 919

Kudos [?]: 217 [0], given: 79

Concentration: Strategy
Schools: Fisher '19 (M)
GPA: 3.71
Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

27 Oct 2016, 00:37
Bunuel wrote:
Let S be a finite set of consecutive multiples of 7. How many terms are there in S?

(1) The sum of the terms in set S is 105. Clearly insufficient. For example, consider S={28, 35, 42} and {49, 56}.

(2) The standard deviation of set S is equal to 3.5. Important property: if we add or subtract a constant to each term in a set SD will not change. From this it follows, that:

Any set with two consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7}, {7, 14}, {14, 21}, {21, 28}, ... will have the same standard deviation.
Any set with three consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14}, {7, 14, 21}, {14, 21, 28}, {21, 28, 35}, ... will have the same standard deviation.
Any set with four consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14, 21}, {7, 14, 21, 28}, {14, 21, 28, 35}, {21, 28, 35, 42}, ... will have the same standard deviation.
...

We know the standard deviation of S is 3.5. We CAN get the standard deviations of {0, 7}, {0, 7, 14}, {0, 7, 14, 21}, ... Only one of them will have the standard deviation of 3.5. So, we can get how many terms are there in the set. Sufficient.

Hope it's clear.

Bunuel One question,how are we sure that one set of consecutive numbers of multiple of 7 will have 3.5 as the S.D. Can't this be the case that none of the sets of multiples of 7 will have a S.D. of 3.5?

Kudos [?]: 217 [0], given: 79

Math Expert
Joined: 02 Sep 2009
Posts: 42571

Kudos [?]: 135384 [1], given: 12691

Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

27 Oct 2016, 01:00
1
KUDOS
Expert's post
Keats wrote:
Bunuel wrote:
Let S be a finite set of consecutive multiples of 7. How many terms are there in S?

(1) The sum of the terms in set S is 105. Clearly insufficient. For example, consider S={28, 35, 42} and {49, 56}.

(2) The standard deviation of set S is equal to 3.5. Important property: if we add or subtract a constant to each term in a set SD will not change. From this it follows, that:

Any set with two consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7}, {7, 14}, {14, 21}, {21, 28}, ... will have the same standard deviation.
Any set with three consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14}, {7, 14, 21}, {14, 21, 28}, {21, 28, 35}, ... will have the same standard deviation.
Any set with four consecutive multiples of 7 will have the same standard deviation. For example, ..., {0, 7, 14, 21}, {7, 14, 21, 28}, {14, 21, 28, 35}, {21, 28, 35, 42}, ... will have the same standard deviation.
...

We know the standard deviation of S is 3.5. We CAN get the standard deviations of {0, 7}, {0, 7, 14}, {0, 7, 14, 21}, ... Only one of them will have the standard deviation of 3.5. So, we can get how many terms are there in the set. Sufficient.

Hope it's clear.

Bunuel One question,how are we sure that one set of consecutive numbers of multiple of 7 will have 3.5 as the S.D. Can't this be the case that none of the sets of multiples of 7 will have a S.D. of 3.5?

On the GMAT, two data sufficiency statements always provide TRUE information and these statements NEVER contradict each other or the stem. Hence if it's said that there is such a set then there must be.

FYI, ..., {0, 7}, {7, 14}, {14, 21}, {21, 28}, ... have the SD of 3.5.
_________________

Kudos [?]: 135384 [1], given: 12691

Non-Human User
Joined: 09 Sep 2013
Posts: 14897

Kudos [?]: 287 [0], given: 0

Re: Let S be a finite set of consecutive multiples of 7. [#permalink]

Show Tags

09 Nov 2017, 01:34
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 287 [0], given: 0

Re: Let S be a finite set of consecutive multiples of 7.   [#permalink] 09 Nov 2017, 01:34
Display posts from previous: Sort by