GRE Prep 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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Two months from now, the population of a colony of insects in a remote
[#permalink]
14 May 2021, 05:49
14 May 2021, 05:49
Expert Reply
1
Bookmarks
00:00
Question Stats:
42% (01:21) correct
57% (01:56) wrong based on 7 sessions
Hide Show timer Statistics
Two months from now, the population of a colony of insects in a remote area will reach 3.2 * 10^4. If the population of the colony doubles every two months, what was the population eight months ago?
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: Two months from now, the population of a colony of insects in a remote
[#permalink]
14 May 2021, 06:41
14 May 2021, 06:41
1
Carcass wrote:
Two months from now, the population of a colony of insects in a remote area will reach 3.2 * 10^4. If the population of the colony doubles every two months, what was the population eight months ago?
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
Let's use a growth table to work backwards
If the population DOUBLES every 2 months we travel into the future, we can also say that the population is HALVED every 2 months we travel into the past
2 months from now: population = (3.2)(10^4)
Now: population = (1/2)(3.2)(10^4) = (1.6)(10^4)
2 months ago: population = (1/2)(1.6)(10^4) = (0.8)(10^4)
4 months ago: population = (1/2)(0.8)(10^4) = (0.4)(10^4)
6 months ago: population = (1/2)(0.4)(10^4) = (0.2)(10^4)
8 months ago: population = (1/2)(0.2)(10^4) = (0.1)(10^4)
(0.1)(10^4) isn't among the answer choices, so let's REWRITE it.
(0.1)(10^4) = (1)(10^-1)(10^4)
= (1)(10^3)
Answer: B
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Given Kudos: 172
Location: India
WE:Education (Education)
Re: Two months from now, the population of a colony of insects in a remote
[#permalink]
14 May 2021, 09:28
14 May 2021, 09:28
1
Carcass wrote:
Two months from now, the population of a colony of insects in a remote area will reach 3.2 * 10^4. If the population of the colony doubles every two months, what was the population eight months ago?
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
a) 3.6 * 10^2
b) 1.0 * 10^3
c) 2.0 * 10^3
d) 1.6 * 10^4
e) 2.6 * 10^4
Let the population after 2 months be \(x\) which is \(3.2(10^4)\)
population at present = \(\frac{x}{2}\)
population 2 months ago = \(\frac{x}{4}\)
population 4 months ago = \(\frac{x}{8}\)
population 6 months ago = \(\frac{x}{16}\)
population 8 months ago = \(\frac{x}{32}\)
Therefore, \(\frac{3.2(10^4)}{32} = \frac{32(10^3)}{32} = 10^3\)
Hence, option B
