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

 It is currently 21 Oct 2019, 13:52 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

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.  LCM of a number

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

Hide Tags

Intern  Joined: 03 Sep 2015
Posts: 1
LCM of a number  [#permalink]

Show Tags

Dear All,

May be this is a stupid question by I am really stuck on it. Im quickly going trough MGMAT foundation of math 5th edition and on page 79 of this book there is following question:

If x is divisible by 8,12, and 45, what is the largest number that x must be divisible by? The answer shows that one needs to find LCM of a number which is a simple task. LCM is thus 360. However, if we check the answer and assume that x=720 and it is really divisible by 8,12, and 45 then 360 is not the largest number 720 must be divisible by. 720 is divisible by 720 either. what do you think?

Thanks and regards
Senior Manager  P
Status: Manager
Joined: 02 Nov 2018
Posts: 280
LCM of a number  [#permalink]

Show Tags

The question is equivalent to what is the lCM of 8,12, and 45
the answer is 360.
LCM means Least common multiple .
So we only find least common number
_________________
Give a kudos if u find my post helpful. kudos motivates active discussions Originally posted by Noshad on 19 Mar 2019, 09:26.
Last edited by Noshad on 29 Mar 2019, 02:10, edited 1 time in total.
VP  V
Joined: 30 Jan 2016
Posts: 1160
LCM of a number  [#permalink]

Show Tags

Hi Jahangir86,

Lowest Common Multiple - LCM. For example, the lowest common multiple of 2 and 3 is 6. No number lower than 6 is divisible by both 2 and 3.
In your case, 360 is divisible by each of the numbers: 8, 12, and 45.

https://gmatclub.com/forum/math-number- ... 88376.html
https://gmatclub.com/forum/gmat-math-book-87417.html

Hope this helps!
_________________
Non progredi est regredi
Senior Manager  V
Joined: 25 Dec 2018
Posts: 488
Location: India
Concentration: General Management, Finance
GMAT Date: 02-18-2019
GPA: 3.4
WE: Engineering (Consulting)
Re: LCM of a number  [#permalink]

Show Tags

the answer is 360 not 720
GMAT Tutor G
Joined: 24 Jun 2008
Posts: 1801
Re: LCM of a number  [#permalink]

Show Tags

I'm not sure the above replies addressed your precise question, so I'll try to explain in a different way:

The question asks: "If x is divisible by 8,12, and 45, what is the largest number that x *must* be divisible by?" This is really saying: "if the only thing you know about x is that it is divisible by 8, 12 and 45, what is the largest number you can be completely sure x is divisible by?" Of course, you're right that x could be equal to 720, and then as you say, x would be divisible not only by 360, but also by the larger number 720. But you can't be sure that x is 720, so you can't be sure that x is divisible by 720. Here x could be lots and lots of different numbers -- it might be the case that x = 360, for example, or that x = 1080, among an infinitude of possibilities.

But even though there is an infinite number of possible values of x here, no matter what x is, you can be completely certain that x is divisible by 360.
_________________
GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com
Manhattan Prep Instructor G
Joined: 04 Dec 2015
Posts: 832
GMAT 1: 790 Q51 V49 GRE 1: Q170 V170 Re: LCM of a number  [#permalink]

Show Tags

Jahangir86 wrote:
Dear All,

May be this is a stupid question by I am really stuck on it. Im quickly going trough MGMAT foundation of math 5th edition and on page 79 of this book there is following question:

If x is divisible by 8,12, and 45, what is the largest number that x must be divisible by? The answer shows that one needs to find LCM of a number which is a simple task. LCM is thus 360. However, if we check the answer and assume that x=720 and it is really divisible by 8,12, and 45 then 360 is not the largest number 720 must be divisible by. 720 is divisible by 720 either. what do you think?

Thanks and regards

It's not actually the math that you're having a hard time with! The math is completely correct:

- You're correct that you need to find the LCM of 8, 12, and 45;
- You've correctly calculated the LCM as 360;
- 360 is the correct answer to the question.

The only issue here is in the wording of the problem. It says 'what is the largest number that x must be divisible by.' In other words, x is some number that's divisible by 8, 12, and 45. That means x could be 360, but x could also be 720, 1080, or a lot of other numbers.

You want to know the largest number that all of those possible values are divisible by - in other words, the number that x must be divisible by. x doesn't have to be divisible by 720, since x could be 360, and 360 isn't divisible by 720. But x does have to be divisible by 360.
_________________ Chelsey Cooley | Manhattan Prep | Seattle and Online

My latest GMAT blog posts | Suggestions for blog articles are always welcome!
Intern  Joined: 29 Mar 2019
Posts: 3
Re: LCM of a number  [#permalink]

Show Tags

true answer is 360....
BSchool Moderator G
Joined: 11 Feb 2018
Posts: 296
Location: India
Concentration: General Management, Finance
GMAT 1: 690 Q47 V37 GMAT 2: 710 Q50 V36 GMAT 3: 750 Q50 V42 Re: LCM of a number  [#permalink]

Show Tags

Coincidentally, you would not believe, I had the precise same doubt yesterday.The answer could be infinity.But I hope you got the concept behind that question!!!! Re: LCM of a number   [#permalink] 29 Mar 2019, 02:29
Display posts from previous: Sort by

LCM of a number

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

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