GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 19 Oct 2019, 23:31 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  At the start of an experiment, a certain population consisted of 3

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Math Expert V
Joined: 02 Sep 2009
Posts: 58445
At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

3
29 00:00

Difficulty:   5% (low)

Question Stats: 91% (01:26) correct 9% (01:52) wrong based on 1198 sessions

HideShow timer Statistics

At the start of an experiment, a certain population consisted of 3 animals. At the end of each month after the start of the experiment, the population size was double its size at the beginning of that month. Which of the following represents the population size at the end of 10 months?

(A) 2^3
(B) 3^2
(C) 2(3^10)
(D) 3(2^10)
(E) 3(10^2)

Kudos for a correct solution.

_________________
Verbal Forum Moderator V
Status: Greatness begins beyond your comfort zone
Joined: 08 Dec 2013
Posts: 2401
Location: India
Concentration: General Management, Strategy
Schools: Kelley '20, ISB '19
GPA: 3.2
WE: Information Technology (Consulting)
At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

4
3
At time when the experiment started , Population N = 3
At end of the first month , Population N1= 3x2 = 6
At end of the second month , Population N2= 6x2 = 12 =$$3 * 2^{2}$$

At the end of nth month , Population Nn = $$3 * 2^{n}$$

Answer D when n =10
_________________
When everything seems to be going against you, remember that the airplane takes off against the wind, not with it. - Henry Ford
The Moment You Think About Giving Up, Think Of The Reason Why You Held On So Long
General Discussion
Senior Manager  B
Joined: 10 Mar 2013
Posts: 465
Location: Germany
Concentration: Finance, Entrepreneurship
Schools: WHU MBA"20 (A)
GMAT 1: 580 Q46 V24 GPA: 3.88
WE: Information Technology (Consulting)
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

1
3*2^n where n is the #of month --> 3*2^10 Answer (D)
_________________
When you’re up, your friends know who you are. When you’re down, you know who your friends are.

Share some Kudos, if my posts help you. Thank you !

800Score ONLY QUANT CAT1 51, CAT2 50, CAT3 50
GMAT PREP 670
MGMAT CAT 630
KAPLAN CAT 660
SVP  V
Status: It's near - I can see.
Joined: 13 Apr 2013
Posts: 1687
Location: India
Concentration: International Business, Operations
Schools: INSEAD Jan '19
GPA: 3.01
WE: Engineering (Real Estate)
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

1
Bunuel wrote:
At the start of an experiment, a certain population consisted of 3 animals. At the end of each month after the start of the experiment, the population size was double its size at the beginning of that month. Which of the following represents the population size at the end of 10 months?

(A) 2^3
(B) 3^2
(C) 2(3^10)
(D) 3(2^10)
(E) 3(10^2)

Kudos for a correct solution.

My Solution:

At the end of every month the population size doubles, so,

After 10 months the population becomes 3072 (3,6,12,24,48,96,192,384,768,1536,3072)

Then find the prime factors of 3072 i.e 3 (2^10) Option D

_________________
"Do not watch clock; Do what it does. KEEP GOING."
Manager  S
Joined: 26 Dec 2012
Posts: 144
Location: United States
Concentration: Technology, Social Entrepreneurship
WE: Information Technology (Computer Software)
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

3
At the beginning of the month the number is 3;
At the end of 1st month number is 3*2
At the end of 2nd month number is 3*2^2
hence at the end of 10th month =3*2^10
Hence answer is D
Manager  P
Joined: 01 Mar 2015
Posts: 69
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

1
population at starting of experiment = 3
at the end of 1st month population = 3 * 2
at the end of 10th month population = 3 * 2^10

Manager  B
Joined: 13 Feb 2011
Posts: 79
At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

Common ratio of increase = 2 and doubling started from end of first month, therefore nth term will be provided by $$initialvalue*r^n$$, i.e. in this case 3*2^10.
Manager  B
Joined: 08 Sep 2015
Posts: 62
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

1
A very simple formula that always helps me with these types of questions:

Final population = S * P ^ (t/i)
S -> starting population
P -> progression (2 - doubles, 3- triples etc.)
t -> time
i -> interval

In our case it is a simple solution, which is : Final population = 3 * 2 ^ (10/1)
so it is 3 * 2^10 -> D
EMPOWERgmat Instructor V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15287
Location: United States (CA)
GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

Hi All,

This is a great 'concept' question - if you recognize the concept involved, then you don't have to do any actual math to solve this problem. If you're not sure how the math 'works' however, you can still use a bit of 'brute force' to define the pattern involved and still get the correct answer.

We're told that a population starts with 3 animals and at the end of each month, the population DOUBLES. We're asked for the size of the population at the end of 10 months.

Based on the 'growth' that's defined, we can list out the first few months worth of data for reference....

Start = 3 animals
Mo. 1 = 3(2) = 6 animals
Mo. 2 = 6(2) = 12 animals
Mo. 3 = 12(2) = 24 animals
Etc.

Notice how each month we multiply the prior month by TWO. That is the pattern involved. We start with 3, then multiply by 2 over-and-over. Since there are 10 months, there will be 10 "multiply by 2s", so the correct answer must be....

GMAT assassins aren't born, they're made,
Rich
_________________
Manager  S
Status: On a 600-long battle
Joined: 22 Apr 2016
Posts: 136
Location: Hungary
Schools: Erasmus '19
GMAT 1: 410 Q18 V27 GMAT 2: 490 Q35 V23 Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

BPHASDEU wrote:
A very simple formula that always helps me with these types of questions:

Final population = S * P ^ (t/i)
S -> starting population
P -> progression (2 - doubles, 3- triples etc.)
t -> time
i -> interval

In our case it is a simple solution, which is : Final population = 3 * 2 ^ (10/1)
so it is 3 * 2^10 -> D

$$Final\quad Population\quad =\quad { S\ast P }^{ \left( \frac { t }{ i } \right) }$$

Very useful - I did not recognize the pattern and ended up doubling the values until the 10th month. Then I prime factorized 3072 and when I saw 1024, I knew there was an easier way to solve it (Actually, I had known it from the very beginning but just couldn't figure it out).
_________________
"When the going gets tough, the tough gets going!"

|Welcoming tips/suggestions/advices (you name it) to help me achieve a 600|
Target Test Prep Representative D
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 8109
Location: United States (CA)
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

3
Bunuel wrote:
At the start of an experiment, a certain population consisted of 3 animals. At the end of each month after the start of the experiment, the population size was double its size at the beginning of that month. Which of the following represents the population size at the end of 10 months?

(A) 2^3
(B) 3^2
(C) 2(3^10)
(D) 3(2^10)
(E) 3(10^2)

We are given that a certain population consisted of 3 animals and that at the end of each month after the start of the experiment, the population size was double what it had been at the beginning of that month. Thus:

End of Month 1 = 3 x 2 = 3 x 2^1

End of Month 2 = 3 x 2 x 2 = 3 x 2^2

End of Month 3 = 3 x 2 x 2 x 2 = 3 x 2^3

We see that after each month the value increases by a factor of two. Thus:

End of Month 10 = 3 x 2^10

_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Director  G
Joined: 02 Sep 2016
Posts: 649
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

2
I think its a GP:
3*2, 3*2*2, 3*2*2,.....................

First term= 6
Common ratio= 2

10th term= first term*common ratio^(n-1)
= 6*2^9
=2*3*2^9
=3*2^10
_________________
Help me make my explanation better by providing a logical feedback.

If you liked the post, HIT KUDOS !!

Don't quit.............Do it.
Manager  G
Joined: 07 Jun 2017
Posts: 161
Location: India
Concentration: Technology, General Management
GMAT 1: 660 Q46 V38 GPA: 3.6
WE: Information Technology (Computer Software)
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

each month doubled means for each month multiply by 2
so 3*(2*2*2*10times)
3*(2^10)
_________________
Regards,
Naveen
email: nkmungila@gmail.com
Please press kudos if you like this post
Intern  B
Joined: 05 Feb 2017
Posts: 39
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

End of 1st Month population =3*2

End of 2nd Month population =3*2*2

Therefore at the end of 10 th Month it will be
3*(2^10)

Hence D

Sent from my iPhone using GMAT Club Forum
Non-Human User Joined: 09 Sep 2013
Posts: 13276
Re: At the start of an experiment, a certain population consisted of 3  [#permalink]

Show Tags

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.
_________________ Re: At the start of an experiment, a certain population consisted of 3   [#permalink] 31 Aug 2019, 07:30
Display posts from previous: Sort by

At the start of an experiment, a certain population consisted of 3

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne  