Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 27 Apr 2015, 10:37

### 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

# Population of a bacteria colony doubles every day. If it was

Author Message
TAGS:
CEO
Joined: 21 Jan 2007
Posts: 2764
Location: New York City
Followers: 9

Kudos [?]: 348 [0], given: 4

Population of a bacteria colony doubles every day. If it was [#permalink]  12 Nov 2007, 11:31
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?
CEO
Joined: 21 Jan 2007
Posts: 2764
Location: New York City
Followers: 9

Kudos [?]: 348 [0], given: 4

Re: doubling [#permalink]  12 Nov 2007, 11:37
Ravshonbek wrote:
bmwhype2 wrote:
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?

3*2^6=64*3=192

Can you explain the numbers?

A. What if it triples instead of doubles?
B. What if it doubles and started 4 days ago?
C. What if it triples and started 3 days ago?
VP
Joined: 09 Jul 2007
Posts: 1108
Location: London
Followers: 6

Kudos [?]: 73 [0], given: 0

Re: doubling [#permalink]  12 Nov 2007, 11:43
bmwhype2 wrote:
Ravshonbek wrote:
bmwhype2 wrote:
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?

3*2^6=64*3=192

Can you explain the numbers?

A. What if it triples instead of doubles?
B. What if it doubles and started 4 days ago?
C. What if it triples and started 3 days ago?

as you know
Double=multiplying by 2
Tripple=multiplying by 3

A. ((((3)*3)*3)....)*3^n = 3*3^6; n=6-number of days
B. 3*2^4=3*16
C. 3*3^3=3*27
CEO
Joined: 21 Jan 2007
Posts: 2764
Location: New York City
Followers: 9

Kudos [?]: 348 [0], given: 4

Re: doubling [#permalink]  16 Nov 2007, 01:03
Ravshonbek wrote:
bmwhype2 wrote:
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?

3*2^6=64*3=192

why do u multiply it again by 3?
Manager
Joined: 20 Sep 2006
Posts: 58
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: doubling [#permalink]  16 Nov 2007, 03:27
Ravshonbek wrote:
bmwhype2 wrote:
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?

3*2^6=64*3=192

Shouldnt the formula for this case be 3 x 2^n-1
where n=6

First day = 3
Second day = 3x2^1
Third day = 3x2^2
.
.
Sixth day = 3x2^5 = 96
Intern
Joined: 14 Nov 2007
Posts: 10
Followers: 0

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

Re: doubling [#permalink]  16 Nov 2007, 03:51
saviop wrote:
Ravshonbek wrote:
bmwhype2 wrote:
Population of a bacteria colony doubles every day. If it was started 6 days ago when 3 bacteria were born in a deserted colony and each bacteria lives for 12 days, how large is the colony today?

3*2^6=64*3=192

Shouldnt the formula for this case be 3 x 2^n-1
where n=6

First day = 3
Second day = 3x2^1
Third day = 3x2^2
.
.
Sixth day = 3x2^5 = 96

I agree with this. 192 will be on the 7th day. The answer is 96
Director
Joined: 26 Jul 2007
Posts: 541
Schools: Stern, McCombs, Marshall, Wharton
Followers: 5

Kudos [?]: 117 [0], given: 0

bmwhype2 wrote:
OA is 96

I dont see how the answer is 96.

If 6 days ago there were 3, then
5 days ago there were 6, then
4 days ago there were 12, then
3 days ago there were 24, then
2 days ago there were 48, then
1 day ago there were 96, then
Today there are 192.

Six days ago means today is the 7th day.
CEO
Joined: 21 Jan 2007
Posts: 2764
Location: New York City
Followers: 9

Kudos [?]: 348 [0], given: 4

gixxer1000 wrote:
bmwhype2 wrote:
OA is 96

I dont see how the answer is 96.

If 6 days ago there were 3, then
5 days ago there were 6, then
4 days ago there were 12, then
3 days ago there were 24, then
2 days ago there were 48, then
1 day ago there were 96, then
Today there are 192.

Six days ago means today is the 7th day.

sorry. you are correct. i was looking at the variation of this question.
Similar topics Replies Last post
Similar
Topics:
17 A certain bacteria colony doubles in size every day for 20 13 12 Dec 2012, 12:42
3 A certain bacteria colony doubles in size every day for 20 5 30 Mar 2012, 01:35
1 The population of a bacteria colony doubles every day. If it was start 16 04 Jun 2011, 02:53
A colony of bacteria doubles every morning while every 8 19 Dec 2007, 12:42
The population of a bacteria culture doubles every 2 2 24 Aug 2006, 03:28
Display posts from previous: Sort by