Last visit was: 30 Apr 2026, 01:20 It is currently 30 Apr 2026, 01:20
Home
Messages
Tests
Schools
Events
Close
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
Your Progress

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 30 Apr 2026
Posts: 109,994
Own Kudos:
812,032
Given Kudos: 105,957
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,994
Kudos: 812,032
A certain jar contains n amoebas at 8:00. After every hour, each of 09 May 2025, 00:30
Kudos
Add Kudos
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

55% (hard)

Question Stats:

65% (02:02) correct 35% (02:25) wrong based on 112 sessions

History

Date
Time
Result
Not Attempted Yet
A certain jar contains n amoebas at 8:00. After every hour, each of the amoebas in the jar splits into 2 amoebas. At the end of every two hours, after splitting, 3 amoebas die. How many amoebas, in terms of n, will be in the jar at 12:00?

(A) n
(B) 4n - 9
(C) 16n - 15
(D) 16n - 12
(E) 4n + 7

­

Gentle note to all experts and tutors: Please refrain from replying to this question until the Official Answer (OA) is revealed. Let students attempt to solve it first. You are all welcome to contribute posts after the OA is posted. Thank you all for your cooperation!
ShowHide Answer
Official Answer
C
avatar
ManifestDreamMBA
avatar
Joined: 17 Sep 2024
Last visit: 21 Feb 2026
Posts: 1,387
Own Kudos:
899
 [1]
Given Kudos: 243
Posts: 1,387
Kudos: 899
 [1]
A certain jar contains n amoebas at 8:00. After every hour, each of 09 May 2025, 04:58
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
TimeNumber
8:00n
9:002n
10:004n-3
11:008n-6
12:0016n-12-3 = 16n-15


Answer is 16n-15
Bunuel
A certain jar contains n amoebas at 8:00. After every hour, each of the amoebas in the jar splits into 2 amoebas. At the end of every two hours, after splitting, 3 amoebas die. How many amoebas, in terms of n, will be in the jar at 12:00?

(A) n
(B) 4n - 9
(C) 16n - 15
(D) 16n - 12
(E) 4n + 7

­

Gentle note to all experts and tutors: Please refrain from replying to this question until the Official Answer (OA) is revealed. Let students attempt to solve it first. You are all welcome to contribute posts after the OA is posted. Thank you all for your cooperation!
Show more
User avatar
kingbucky
User avatar
Joined: 28 Jul 2023
Last visit: 22 Apr 2026
Posts: 498
Own Kudos:
586
Given Kudos: 329
Location: India
Products:
My Reviews
Posts: 498
Kudos: 586
A certain jar contains n amoebas at 8:00. After every hour, each of 11 May 2025, 10:15
Kudos
Add Kudos
Bookmarks
Bookmark this Post
At the end of every two hours, after splitting, 3 amoebas die. ( and not "At the end of every two hours, 3 amoebas die"). That is, in my understanding, the death of 3 amoebas happen every hour starting with 10:00.

TimeNumber
8:00nstart
9:002nsplit
10:004n-3split and 2 hours after split at 8, 3 die
11:008n-9split and 2 hours after split at 9, 3 die
12:0016n-21split and 2 hours after split at 11, 3 die

Bunuel Now, this is my line of thinking, can you tell me what I'm missing ? Shouldn't the OA be 16n-21 ?
User avatar
ODST117
User avatar
Joined: 15 Aug 2024
Last visit: 27 Jan 2026
Posts: 173
Own Kudos:
88
 [2]
Given Kudos: 149
Posts: 173
Kudos: 88
 [2]
A certain jar contains n amoebas at 8:00. After every hour, each of 11 May 2025, 12:58
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I'm not Bunuel but I think I can alleviate your confusion.
The question states "at the end of every two hours, after splitting, 3 amoebas die", which means, after every two hour interval, in addition to the amoebas doubling every hour, three of them also die. The setup starts at 8:00 and after the first two hour interval, we come to 10:00, then after the next two hour interval, we come to 12:00.
So, at 8:00 the population is \(n\).
At 9:00, the population is \(2n\).
At 10:00 (which is the end of the first two hour interval) the population doubles from what it was at 9:00 and 3 amoeba die, i.e, \(2(2n)-3 = 4n-3\).
At 11:00 it's \(2(4n-3) = 8n-6\).
Then, finally, at 12:00 (which is the end of the second two hour interval), the population doubles from what it was at 11:00 and 3 amoeba die, i.e, \(2(8n-6)-3 = 16n-12-3 = 16n-15\).
kingbucky
At the end of every two hours, after splitting, 3 amoebas die. ( and not "At the end of every two hours, 3 amoebas die"). That is, in my understanding, the death of 3 amoebas happen every hour starting with 10:00.

TimeNumber
8:00nstart
9:002nsplit
10:004n-3split and 2 hours after split at 8, 3 die
11:008n-9split and 2 hours after split at 9, 3 die
12:0016n-21split and 2 hours after split at 11, 3 die

Bunuel Now, this is my line of thinking, can you tell me what I'm missing ? Shouldn't the OA be 16n-21 ?
Show more
User avatar
kingbucky
User avatar
Joined: 28 Jul 2023
Last visit: 22 Apr 2026
Posts: 498
Own Kudos:
586
 [1]
Given Kudos: 329
Location: India
Products:
My Reviews
Posts: 498
Kudos: 586
 [1]
A certain jar contains n amoebas at 8:00. After every hour, each of 11 May 2025, 13:12
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
"At the end of every two hours, after splitting, 3 amoebas die"....
Why dont we interpret that as, at the end of every two hours after the splitting has occured, 3 amoebas die ?

ODST117
I'm not Bunuel but I think I can alleviate your confusion.
The question states "at the end of every two hours, after splitting, 3 amoebas die", which means, after every two hour interval, in addition to the amoebas doubling every hour, three of them also die. The setup starts at 8:00 and after the first two hour interval, we come to 10:00, then after the next two hour interval, we come to 12:00.
So, at 8:00 the population is \(n\).
At 9:00, the population is \(2n\).
At 10:00 (which is the end of the first two hour interval) the population doubles from what it was at 9:00 and 3 amoeba die, i.e, \(2(2n)-3 = 4n-3\).
At 11:00 it's \(2(4n-3) = 8n-6\).
Then, finally, at 12:00 (which is the end of the second two hour interval), the population doubles from what it was at 11:00 and 3 amoeba die, i.e, \(2(8n-6)-3 = 16n-12-3 = 16n-15\).
kingbucky
At the end of every two hours, after splitting, 3 amoebas die. ( and not "At the end of every two hours, 3 amoebas die"). That is, in my understanding, the death of 3 amoebas happen every hour starting with 10:00.

TimeNumber
8:00nstart
9:002nsplit
10:004n-3split and 2 hours after split at 8, 3 die
11:008n-9split and 2 hours after split at 9, 3 die
12:0016n-21split and 2 hours after split at 11, 3 die

Bunuel Now, this is my line of thinking, can you tell me what I'm missing ? Shouldn't the OA be 16n-21 ?
Show more
Moderators:
Bunuel
Math Expert
109994 posts
Krunaal
Tuck School Moderator
852 posts