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

It is currently 28 Jul 2014, 16:56

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

GMAT iphone app - question 85

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 12 Jul 2010
Posts: 9
Followers: 0

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

GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 09:59
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

50% (03:18) correct 50% (02:44) wrong based on 4 sessions
Hi everybody,

In the iphone app : the quantitative set - question 85 :
How many three digit integers are not divisible by 3 ?

Answer seems to be 600. But i don't understand how !

I agree that 300 3-digit integers are divisible by 3, but why 600 are not ! what about the last 100's ?

Why it is not the rest : 700 ?

Thanks for your help.

Fred
[Reveal] Spoiler: OA
Intern
Intern
avatar
Joined: 03 Aug 2010
Posts: 27
Schools: Sloan '14 (M)
GRE 1: 337 Q168 V169
WE: Engineering (Energy and Utilities)
Followers: 0

Kudos [?]: 9 [0], given: 0

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 11:50
The numbers from 1-99 are not 3 digits. Only numbers 100-999 are 3 digit (this is 900 numbers total).
Senior Manager
Senior Manager
User avatar
Status: Time to step up the tempo
Joined: 24 Jun 2010
Posts: 411
Location: Milky way
Schools: ISB, Tepper - CMU, Chicago Booth, LSB
Followers: 7

Kudos [?]: 108 [0], given: 50

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 16:49
funboard70 wrote:
Hi everybody,

In the iphone app : the quantitative set - question 85 :
How many three digit integers are not divisible by 3 ?

Answer seems to be 600. But i don't understand how !

I agree that 300 3-digit integers are divisible by 3, but why 600 are not ! what about the last 100's ?

Why it is not the rest : 700 ?

Thanks for your help.

Fred


My attempt:

3 digit integers -- 100 to 999.

Total there are ((999 - 100) +1) = 900 numbers.

Now for every 10 numbers -- 101, 102, 103,104, 105, 106, 107, 108, 109, 110 -- only 3 are divisible by 3 (i.e,. 102, 105, 108) and 7 numbers are not.

Hence for 900 numbers, only (7/10)*900 numbers are not divisible by 3.

=> 630 numbers are not divisible by 3.
_________________

:good Support GMAT Club by putting a GMAT Club badge on your blog :thanks

Manager
Manager
avatar
Joined: 20 Mar 2010
Posts: 84
Followers: 2

Kudos [?]: 46 [0], given: 1

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 18:21
funboard70 wrote:
Hi everybody,

In the iphone app : the quantitative set - question 85 :
How many three digit integers are not divisible by 3 ?

Answer seems to be 600. But i don't understand how !

I agree that 300 3-digit integers are divisible by 3, but why 600 are not ! what about the last 100's ?

Why it is not the rest : 700 ?

Thanks for your help.

Fred
.

Here is how i approached it.
Total no of 3 digit integers = 9*10*10 = 900 (First digit can't be zero)
Any multiples of 3 are divisible by 3. So if we can find the no of multiples of 3 between 100 and 999 that no can be subtracted from 900 to get the 3 digit integers not divisible by 3.
There are 333 multiples of 3 < 1000 (999 is the greatest multiple of 3 under 1000 and 999/3 =333)
There are 33 multiples of 3 < 100 (99 is the greatest multiple of 3 under 100 and 99/3 =33)
So There are 333-33=300 multiples of 3 between 100 and 999 and 900-300=600 3 digit integers which are not divisible by 3.
_________________

___________________________________
Please give me kudos if you like my post

Director
Director
avatar
Status: Apply - Last Chance
Affiliations: IIT, Purdue, PhD, TauBetaPi
Joined: 17 Jul 2010
Posts: 693
Schools: Wharton, Sloan, Chicago, Haas
WE 1: 8 years in Oil&Gas
Followers: 14

Kudos [?]: 69 [0], given: 15

GMAT Tests User
Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 19:17
well since there are 900 3 digit numbers, and every 3rd number is divisible by 3, then the number of numbers divisible by 3 = 900/3 does this approach make sense? by the same token the number of numbers divisible by 4 = 900/4 = 225, by 5 = 900/5=180... does this work in general?
_________________

Consider kudos, they are good for health

Intern
Intern
avatar
Joined: 12 Jul 2010
Posts: 9
Followers: 0

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

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 20:18
brau0300 wrote:
The numbers from 1-99 are not 3 digits. Only numbers 100-999 are 3 digit (this is 900 numbers total).


Thanks Brau... Stupid mistake that i made...
Intern
Intern
avatar
Joined: 12 Jul 2010
Posts: 9
Followers: 0

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

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 20:26
mainhoon wrote:
well since there are 900 3 digit numbers, and every 3rd number is divisible by 3, then the number of numbers divisible by 3 = 900/3 does this approach make sense? by the same token the number of numbers divisible by 4 = 900/4 = 225, by 5 = 900/5=180... does this work in general?


Hi,

In fact, it is not a general rule ! Ex : 900 / 7 = 128.51...
How do i approach this kind of prob:
(larger multiple - smaller multiple) / multiple + 1

with the example of 3
Larger Multiple : 999
Smaller multiple : 102
So (999 - 102) / 3 + 1 = 300

Example of 5 :
Larger Multiple : 995
Smaller multiple : 100
Therefore : (995 - 100) / 5 + 1 = 180

Another way to check is to find the first and the result of the division
Ex with 3
102 / 3 = 34
999 / 3 = 333
333 - 34 + 1 = 300

Hope it's clear...

Fred
Intern
Intern
avatar
Joined: 12 Jul 2010
Posts: 9
Followers: 0

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

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 20:29
ezhilkumarank wrote:
funboard70 wrote:
Hi everybody,

In the iphone app : the quantitative set - question 85 :
How many three digit integers are not divisible by 3 ?

Answer seems to be 600. But i don't understand how !

I agree that 300 3-digit integers are divisible by 3, but why 600 are not ! what about the last 100's ?

Why it is not the rest : 700 ?

Thanks for your help.

Fred


My attempt:

3 digit integers -- 100 to 999.

Total there are ((999 - 100) +1) = 900 numbers.

Now for every 10 numbers -- 101, 102, 103,104, 105, 106, 107, 108, 109, 110 -- only 3 are divisible by 3 (i.e,. 102, 105, 108) and 7 numbers are not.

Hence for 900 numbers, only (7/10)*900 numbers are not divisible by 3.

=> 630 numbers are not divisible by 3.


Hi,

In Fact you can't use the solution of choosing 10 numbers and extrapolate after.
What about 180 till 189 ? there are 4 integers divisible by 3... not 3

Anyway thanks for your help !

Fred
Intern
Intern
avatar
Joined: 12 Jul 2010
Posts: 9
Followers: 0

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

Re: GMAT iphone app - question 85 [#permalink] New post 09 Aug 2010, 20:32
crack700 wrote:
funboard70 wrote:
Hi everybody,

In the iphone app : the quantitative set - question 85 :
How many three digit integers are not divisible by 3 ?

Answer seems to be 600. But i don't understand how !

I agree that 300 3-digit integers are divisible by 3, but why 600 are not ! what about the last 100's ?

Why it is not the rest : 700 ?

Thanks for your help.

Fred
.

Here is how i approached it.
Total no of 3 digit integers = 9*10*10 = 900 (First digit can't be zero)
Any multiples of 3 are divisible by 3. So if we can find the no of multiples of 3 between 100 and 999 that no can be subtracted from 900 to get the 3 digit integers not divisible by 3.
There are 333 multiples of 3 < 1000 (999 is the greatest multiple of 3 under 1000 and 999/3 =333)
There are 33 multiples of 3 < 100 (99 is the greatest multiple of 3 under 100 and 99/3 =33)
So There are 333-33=300 multiples of 3 between 100 and 999 and 900-300=600 3 digit integers which are not divisible by 3.



Humm another way to find the solution...
Thanks for your help !

Fred
Intern
Intern
avatar
Joined: 23 May 2011
Posts: 1
Followers: 0

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

Re: GMAT iphone app - question 85 [#permalink] New post 24 May 2011, 02:18
hi...first of all for division of 3 rule changing digits would not make the differce as far as the sum of the digits is divisible by 3. Hence the change that the Q mentions will not have any difference.

Now the total nos divisible by 3 are : (400-310)/3= 30 . Here the inclusion of 310 does not come into the picture because it is not divisible by 3. If the first no. would have been say 309 then we would have to add +1 to 30. I hope this clears the doubt....
VP
VP
avatar
Status: There is always something new !!
Affiliations: PMI,QAI Global,eXampleCG
Joined: 08 May 2009
Posts: 1365
Followers: 10

Kudos [?]: 132 [0], given: 10

GMAT Tests User
Re: GMAT iphone app - question 85 [#permalink] New post 24 May 2011, 02:51
total integers = 1000-100 = 900
integers divisible by 3 = 999= 102 + (n-1) * 3
n=300.

thus 600 = 900-300
_________________

Visit -- http://www.sustainable-sphere.com/
Promote Green Business,Sustainable Living and Green Earth !!

Intern
Intern
avatar
Joined: 13 Mar 2011
Posts: 11
Followers: 0

Kudos [?]: 1 [0], given: 4

GMAT ToolKit User
Re: GMAT iphone app - question 85 [#permalink] New post 27 May 2011, 09:38
Using AP(like in the post above mine) to solve such question is the quickest way..

@ezhilkumarank good approach
_________________

How about some KUDOS...ey??!!

Manager
Manager
avatar
Joined: 25 Sep 2010
Posts: 85
Schools: HBS, LBS, Wharton, Kelloggs, Booth
Followers: 0

Kudos [?]: 2 [0], given: 15

Re: GMAT iphone app - question 85 [#permalink] New post 20 Jul 2011, 06:18
I got 600 too.
My method is:

no. of 3 digit numbers div. by 3 => range from 100 to 999
we can also say that no. of 3 digit numbers range from 102 to 999 inclusive.
hence, we use the formula:
no. of digits = (Last - First)/increment + 1
= (999 - 102)/3 + 1 = 300
Similarly, we find number of integers from 100 to 999;
no. of digits = Last - First + 1
= 999 - 100 + 1
= 900
No. of integers NOT div. by 3 = Total no. of integers - No. of integers div. by 3
= 900 - 300
= 600
Re: GMAT iphone app - question 85   [#permalink] 20 Jul 2011, 06:18
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic GMAT Pill iPhone App v1.0 Released! GMATPill 0 04 Dec 2012, 22:01
Experts publish their posts in the topic Overlap between GmatClub tests and Iphone/Ipad app gdk26 2 30 May 2011, 09:26
Experts publish their posts in the topic GMAT Toolkit App - Ipad/Iphone App asmit123 8 08 Mar 2011, 22:45
Experts publish their posts in the topic GMAT Toolkit iPhone app - Bug - or is it my iPhone ? hideyoshi 1 07 Apr 2010, 07:32
1 Experts publish their posts in the topic iPhone Apps and Podcasts to help with GMAT Prep yangsta8 7 03 Nov 2009, 22:13
Display posts from previous: Sort by

GMAT iphone app - question 85

  Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.