Last visit was: 23 Apr 2024, 15:30 It is currently 23 Apr 2024, 15:30
Decision Tracker
My Rewards
New comers' posts
New posts
Unanswered

Close

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

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 GRE 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
PREVIOUS TOPIC
NEXT TOPIC

The average (arithmetic mean) age of the buildings on a cert

Tags :
Find Similar Topics  About  Add a Tag

Show Tags
Hide Tags

User avatar
sandy
Retired Moderator
Joined: 07 Jun 2014
Posts: 4810
Own Kudos [?]: 10616 [5]
Given Kudos: 0
GRE 1: Q167 V156
WE:Business Development (Energy and Utilities)
Send PM
The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   30 Aug 2018, 07:46
1
Expert Reply
4
Bookmarks
00:00

Question Stats:

48% (02:54) correct 51% (01:54) wrong based on 78 sessions

Hide Show timer Statistics

The average (arithmetic mean) age of the buildings on a certain city block is greater than 40 years old. If four of the buildings were built two years ago and none of the buildings are more than 80 years old, which of the following could be the number of buildings on the block?

Indicate all such numbers.

A. 4
B. 6
C. 8
D. 11
E. 40
ShowHide Answer
Official Answer
C,D,E
Most Helpful Community Reply
avatar
dare90
Intern
Intern
Joined: 14 May 2019
Posts: 31
Own Kudos [?]: 50 [8]
Given Kudos: 36
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   27 Mar 2020, 00:41
8
sandy wrote:
The average (arithmetic mean) age of the buildings on a certain city block is greater than 40 years old. If four of the buildings were built two years ago and none of the buildings are more than 80 years old, which of the following could be the number of buildings on the block?

Indicate all such numbers.

A. 4
B. 6
C. 8
D. 11
E. 40



let the number of buildings = n
number of buildings built 2yrs ago = 4 ;total age in yrs of 4 buildings = 2*4 = 8
remaining buildings = n-4 ; total age in years of (n-4) buildings = 80(n-4)
number of buildings = 8 + 80(n-4)/n >40
when n=4, 8<40
when n=6, 28<40
when n=8, 41>40
when n=11, 51.64>40
when n=40, 72.2>40
hence, ans is C,D,E
General Discussion
avatar
Arc29
Intern
Intern
Joined: 10 Aug 2018
Posts: 29
Own Kudos [?]: 9 [0]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   31 Aug 2018, 21:03
How to solve it?
please explain
avatar
shivankkhanna
Intern
Intern
Joined: 07 Sep 2018
Posts: 29
Own Kudos [?]: 4 [0]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   12 Sep 2018, 00:50
explanation pls.??
User avatar
D
Carcass
Verbal Expert
Joined: 18 Apr 2015
Posts: 28620
Own Kudos [?]: 33099 [3]
Given Kudos: 25173
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   12 Sep 2018, 07:59
2
Expert Reply
1
Bookmarks
\(40x= (x-4)(80)\)

\(-40x=-320\)

\(x= 7.8\)

x must be at least 8 to bring the average age up over 40.

Hope this helps.

Regards
avatar
jelal123
Manager
Manager
Joined: 08 Dec 2018
Posts: 94
Own Kudos [?]: 69 [0]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   11 Jun 2019, 07:26
1
if (x-4)80=40x, then (x-4)80 keeps average equal to 40 and there are the rest 4 buildings aged 2 years less than others .
Therefore, the value X ( integer as it is building number )decides the range of the number of buildings.
Thank you,
It helps immensely .
regards
avatar
NickBass
Manager
Manager
Joined: 02 Mar 2020
Posts: 54
Own Kudos [?]: 14 [0]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   26 Mar 2020, 15:23
I still don't get how the equation was set up
avatar
Mudslide53
Intern
Intern
Joined: 18 May 2020
Posts: 35
Own Kudos [?]: 58 [2]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   26 May 2020, 18:57
1
1
Bookmarks
I set up the equation differently:

The average age of any set of buildings would be defined as: [total age in years of all the buildings] / [# of buildings]

In this case, we have 4 buildings built 2 years ago (4*2 = 8 years), and we can pretend that the rest of the buildings are 80 years old to solve for the extreme case. Let B be the REST of the buildings. So:

[total age in years of all the buildings] = 8 + 80B.

The total number of buildings will be 4 + B.

Solve for the inequality:

[8+80B]/[B+4] > 40
You'll get
B>3.8

You have to go back and add the remaining 4 buildings back in...

B>3.8+4 --> B>7.8

So, B > 7.8, which makes the answer choices C D and E
avatar
B
lucifer6251
Intern
Intern
Joined: 01 Sep 2021
Posts: 36
Own Kudos [?]: 31 [1]
Given Kudos: 77
Send PM
The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   10 Sep 2021, 02:02
1
Bookmarks
Let, total buildings = x

4 of them are 2 years old, so a total of 4*2 = 8 years old

remaining (x - 4) buildings are at most 80 years old. So in total of (x - 4)*80 years old.

So,
(8 + (x - 4)*80) / x = 40
=> x = 7.8 = 8 (As we have to consider the average greater than 40)

At least 8 buildings are there. So, we can consider the numbers that are greater than or equal to 8.

Ans: C, D, E
avatar
B
Optimist
Intern
Intern
Joined: 29 Aug 2021
Posts: 37
Own Kudos [?]: 14 [0]
Given Kudos: 46
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   19 Sep 2021, 23:25
Carcass wrote:
\(40x= (x-4)(80)\)

\(-40x=-320\)

\(x= 7.8\)

x must be at least 8 to bring the average age up over 40.

Hope this helps.

Regards


Carcass, as per your equation, x equates to 8 and not 7.8. There is some dissonance that needs to be cleared.

Thanks in advance for your clarification!
User avatar
bumpbot
GRE Prep Club Legend
GRE Prep Club Legend
Joined: 07 Jan 2021
Posts: 4411
Own Kudos [?]: 68 [0]
Given Kudos: 0
Send PM
Re: The average (arithmetic mean) age of the buildings on a cert [#permalink] New post   03 Oct 2022, 04:06
Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep 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.
Prep Club for GRE Bot
gmatclubot
[#permalink]
Moderators:
BrushMyQuant
Moderator
1085 posts
VibhuAnurag
GRE Instructor
218 posts

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

Main navigation

Partners

GRE Resources

www.ets.org/gre | About | Terms and Conditions and Privacy Policy | Prep Club for GRE Rules | Contact