It is currently 21 Oct 2017, 18:39

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

At 15:00 there were 20 students in the lab. At 15:03 and

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Director
Director
avatar
Joined: 09 Aug 2006
Posts: 754

Kudos [?]: 256 [0], given: 0

At 15:00 there were 20 students in the lab. At 15:03 and [#permalink]

Show Tags

New post 22 Oct 2007, 23:04
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

At 15:00 there were 20 students in the lab. At 15:03 and every three minutes after that 3 students entered the lab. At 15:10 and every ten minutes after that 8 students left the lab. How many students were in the lab at 15:44?

a) 7
b) 14
c) 25
d) 27
e) 30

Pls. explain.

Kudos [?]: 256 [0], given: 0

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jul 2004
Posts: 5034

Kudos [?]: 438 [0], given: 0

Location: Singapore
 [#permalink]

Show Tags

New post 22 Oct 2007, 23:46
# of students in = [(42-3)/3 + 1]*3 = 14*3 = 42
# of students out = [(40-10)/10 + 1]*8 = 32
Net = 42-32 + 20 = 30

Ans E

Kudos [?]: 438 [0], given: 0

Manager
Manager
avatar
Joined: 01 Oct 2007
Posts: 138

Kudos [?]: 5 [0], given: 0

 [#permalink]

Show Tags

New post 23 Oct 2007, 01:30
ywilfred wrote:
# of students in = [(42-3)/3 + 1]*3 = 14*3 = 42
# of students out = [(40-10)/10 + 1]*8 = 32
Net = 42-32 + 20 = 30

Ans E


ywilfred -- whats the formula u used? very fast it seems..

Kudos [?]: 5 [0], given: 0

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jul 2004
Posts: 5034

Kudos [?]: 438 [0], given: 0

Location: Singapore
 [#permalink]

Show Tags

New post 23 Oct 2007, 01:47
yash500 wrote:
ywilfred wrote:
# of students in = [(42-3)/3 + 1]*3 = 14*3 = 42
# of students out = [(40-10)/10 + 1]*8 = 32
Net = 42-32 + 20 = 30

Ans E


ywilfred -- whats the formula u used? very fast it seems..


We know there's an inflow of students and an outflow of students.

The inflow comes at every 3 minutes after 3:03pm and each interval there are 3 students added in. So between 1544 and 1503, there are 42 minutes. So there're 14 such intervals and therefore 14*3 = 42 students.

The outflow comes at every 10 minutes after 3:10pm and each interval there are 8 students going out. From 1510 to 1540, there will be 4 such intevals and so 4*8 = 32 students are added.

The nett is 20 - 32 + 42 = 30 student.

Regarding my working... I used:

(42/3 + 1) --> the 42 comes from subtracting 1503 from 1542 because for 3 minute intervals, the last whole divisible by 3 is 1542 and the smallest whole number divisible is the start time given as 1503. I'm not sure the principal behind this (or maybe I forgot) but it worked well for me in cases such as..

How many evens between 21 and 10. I will take (20-10)/2 + 1 = 6
How many terms divisible by 3 between 15 and 1. I will take (15-3)/3 + 1 = 5

Kudos [?]: 438 [0], given: 0

Director
Director
avatar
Joined: 09 Aug 2006
Posts: 754

Kudos [?]: 256 [0], given: 0

 [#permalink]

Show Tags

New post 23 Oct 2007, 06:30
ywilfred wrote:
yash500 wrote:
ywilfred wrote:
# of students in = [(42-3)/3 + 1]*3 = 14*3 = 42
# of students out = [(40-10)/10 + 1]*8 = 32
Net = 42-32 + 20 = 30

Ans E


ywilfred -- whats the formula u used? very fast it seems..


We know there's an inflow of students and an outflow of students.

The inflow comes at every 3 minutes after 3:03pm and each interval there are 3 students added in. So between 1544 and 1503, there are 42 minutes. So there're 14 such intervals and therefore 14*3 = 42 students.

The outflow comes at every 10 minutes after 3:10pm and each interval there are 8 students going out. From 1510 to 1540, there will be 4 such intevals and so 4*8 = 32 students are added.

The nett is 20 - 32 + 42 = 30 student.

Regarding my working... I used:

(42/3 + 1) --> the 42 comes from subtracting 1503 from 1542 because for 3 minute intervals, the last whole divisible by 3 is 1542 and the smallest whole number divisible is the start time given as 1503. I'm not sure the principal behind this (or maybe I forgot) but it worked well for me in cases such as..

How many evens between 21 and 10. I will take (20-10)/2 + 1 = 6
How many terms divisible by 3 between 15 and 1. I will take (15-3)/3 + 1 = 5



Thanks for the great explanation! Wish I could work out Math like you :)

Kudos [?]: 256 [0], given: 0

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 16587

Kudos [?]: 273 [0], given: 0

Premium Member
Re: At 15:00 there were 20 students in the lab. At 15:03 and [#permalink]

Show Tags

New post 05 Mar 2017, 05:44
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Kudos [?]: 273 [0], given: 0

Re: At 15:00 there were 20 students in the lab. At 15:03 and   [#permalink] 05 Mar 2017, 05:44
Display posts from previous: Sort by

At 15:00 there were 20 students in the lab. At 15:03 and

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.