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

It is currently 20 Aug 2019, 19:54

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

One wheel rotates once every 3 minutes and another rotates once every

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

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 57155
One wheel rotates once every 3 minutes and another rotates once every  [#permalink]

Show Tags

New post 31 Jul 2019, 23:45
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

96% (00:51) correct 4% (02:11) wrong based on 26 sessions

HideShow timer Statistics

Director
Director
User avatar
P
Joined: 03 Jun 2019
Posts: 955
Location: India
Re: One wheel rotates once every 3 minutes and another rotates once every  [#permalink]

Show Tags

New post 01 Aug 2019, 00:54
Bunuel wrote:
One wheel rotates once every 3 minutes and another rotates once every 7 minutes. If both wheels begin to rotateat the same time, after how many minutes will they both begin a rotation again ?

A. 5
B. 7
C. 14
D. 12
E. 21



Given: One wheel rotates once every 3 minutes and another rotates once every 7 minutes. Both wheels begin to rotate at the same time.

Asked: After how many minutes will they both begin a rotation again ?

After how many minutes will they both begin a rotation again = LCM (3,7) = 21

IMO E
_________________
"Success is not final; failure is not fatal: It is the courage to continue that counts."

Please provide kudos if you like my post. Kudos encourage active discussions.

My GMAT Resources: -

Efficient Learning

Tele: +91-11-40396815
Mobile : +91-9910661622
E-mail : kinshook.chaturvedi@gmail.com
CrackVerbal Quant Expert
User avatar
S
Joined: 12 Apr 2019
Posts: 218
Re: One wheel rotates once every 3 minutes and another rotates once every  [#permalink]

Show Tags

New post 01 Aug 2019, 01:23
We need to calculate the LCM (Least Common Multiple) of 3 and 7 in this question. This is because the time when they will start rotating again at the same time will be the LCM of 3 and 7.

If we make a RED mark on each of the wheels when they are at the starting position:

On the first wheel, this red mark will cross the starting position after every 3 minutes i.e. 3, 6, 9 and so on.
On the second wheel, this red mark will cross the starting position after every 7 minutes i.e. 7, 14, 21 and so on.

If we want them to begin a rotation together, we want both the red marks to be at the starting position at the same time. This happens every 21 minutes, since 21 is the common number in both the lists above.
So, the correct answer option is E.

When you first saw this question, if you were confused whether you have to find out HCF or LCM in this question, ask yourself these questions?

Do I need to divide 3 and 7 into smaller parts? If your answer is yes, then you have to find out the HCF.
Do I need to look at the multiples of 3? If your answer is yes, then you have to find out the LCM.

Clearly, in this question, we are looking at multiples of 3 and 7 and hence we have to find out the LCM. Here are some links to a few of our posts on HCF and LCM.

https://gmatclub.com/forum/factors-multiples-a-simple-way-of-understanding-them-296311.html
https://gmatclub.com/forum/factors-multiples-hcf-lcm-296385.html

Hope this helps!
_________________
Target Test Prep Representative
User avatar
D
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 7411
Location: United States (CA)
Re: One wheel rotates once every 3 minutes and another rotates once every  [#permalink]

Show Tags

New post 06 Aug 2019, 17:40
Bunuel wrote:
One wheel rotates once every 3 minutes and another rotates once every 7 minutes. If both wheels begin to rotateat the same time, after how many minutes will they both begin a rotation again ?

A. 5
B. 7
C. 14
D. 12
E. 21


Since the LCM of 3 and 7 is 21, the wheels will begin a rotation at the same time after 21 minutes.

Answer: E
_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
TTP - Target Test Prep Logo
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

GMAT Club Bot
Re: One wheel rotates once every 3 minutes and another rotates once every   [#permalink] 06 Aug 2019, 17:40
Display posts from previous: Sort by

One wheel rotates once every 3 minutes and another rotates once every

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





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