GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 17 Oct 2018, 00:29

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

How to find numbers inbetween set

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Manager
Manager
User avatar
Joined: 13 Jun 2016
Posts: 118
Location: United States
Concentration: Finance, Technology
How to find numbers inbetween set  [#permalink]

Show Tags

New post 20 Apr 2017, 20:47
Is there a formula to quickly figure out the number of numbers between lets say -40 to 100 that are divisible by 3?
Intern
Intern
avatar
B
Joined: 30 Mar 2017
Posts: 3
How to find numbers inbetween set  [#permalink]

Show Tags

New post 24 Apr 2017, 13:07
Yeah

In your example:
The first number divisible by 3 in your set would be -39 and the last would be 99
step 1: subtract largest divisible number in set by the smallest: 99 - (-39) = 138
step 2: divide the difference by the divisible number: 138 / 3 = 46
step 3: add 1: 46 + 1 = 47 total numbers between 99 and -39 that are divisible by 3

This is easy to see with small numbers
For example:
set = from 7 to 21, we need to find number of numbers divisible by 7
21- 7 = 14
14 / 7 = 2
2 + 1 = 3
Current Student
avatar
P
Joined: 17 Jun 2016
Posts: 515
Location: India
GMAT 1: 720 Q49 V39
GMAT 2: 710 Q50 V37
GPA: 3.65
WE: Engineering (Energy and Utilities)
GMAT ToolKit User Premium Member Reviews Badge
Re: How to find numbers inbetween set  [#permalink]

Show Tags

New post 04 May 2017, 06:58
1
jwang1191 wrote:
Yeah

In your example:
The first number divisible by 3 in your set would be -39 and the last would be 99
step 1: subtract largest divisible number in set by the smallest: 99 - (-39) = 138
step 2: divide the difference by the divisible number: 138 / 3 = 46
step 3: add 1: 46 + 1 = 47 total numbers between 99 and -39 that are divisible by 3

This is easy to see with small numbers
For example:
set = from 7 to 21, we need to find number of numbers divisible by 7
21- 7 = 14
14 / 7 = 2
2 + 1 = 3


Yeah its called sequence & series :

Lets say u need to know how many numbers are there between 40 to 100 that are multiple of 3.

So start with first multiple of 3 after 40. In this case it is 42
and the last multiple of 3 before 100. Its 99.
So the formula is

nth term = first term + (n-1)*d
where d is the difference between each of the consecutive numbers. In this case it is 3
n= number of terms (which is what you are looking for)

So using above formula :
nth term is 99
first term is 42
and d is 3

So 99 = 42 + (n-1)*3
57 = (n-1)*3
n-1 = 19
n = 20

You can cross check by any other method ..

This topic is called Sequence and series which we (Indians) study in 11th grade maths...


Hit kudos if this helps!!!
_________________

Compilation of Blogs by Mike Mcgarry - Magoosh

GMAT Club Bot
Re: How to find numbers inbetween set &nbs [#permalink] 04 May 2017, 06:58
Display posts from previous: Sort by

How to find numbers inbetween set

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| 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®.