It is currently 20 Nov 2017, 12:30

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

An alarm of a certain clock rings every 20 minutes. If the clock's ala

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

Hide Tags

Expert Post
Math Revolution GMAT Instructor
User avatar
P
Joined: 16 Aug 2015
Posts: 4326

Kudos [?]: 3041 [0], given: 0

GPA: 3.82
Premium Member CAT Tests
An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 02:43
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

56% (00:52) correct 44% (00:48) wrong based on 100 sessions

HideShow timer Statistics

An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30
B. 18:00
C. 18:30
D. 19:00
E. 19:30
[Reveal] Spoiler: OA

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo


Last edited by MathRevolution on 18 Aug 2017, 19:54, edited 2 times in total.

Kudos [?]: 3041 [0], given: 0

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132809 [0], given: 12378

Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 02:46
MathRevolution wrote:
An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30
B. 18:00
C. 18:30
D. 19:00
E. 19:30


Similar question: https://gmatclub.com/forum/an-alarm-of- ... 44589.html
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 132809 [0], given: 12378

2 KUDOS received
Intern
Intern
avatar
S
Joined: 22 Apr 2015
Posts: 29

Kudos [?]: 25 [2], given: 62

WE: Business Development (Internet and New Media)
Reviews Badge CAT Tests
Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 03:57
2
This post received
KUDOS
the alarm rings every 20 mins. => d= 20 min= \(\frac{1}{3}\) hr
1st ring at 15:20. => a= 15:20= (15+\(\frac{1}{3}\)) hr=\(\frac{46}{3}\) hr
12th ring= t12= a+(12-1)d= a+11d= \(\frac{46}{3}\)+\(\frac{1}{3}\)= \(\frac{57}{3}\) hr= 19 hr= 19:00

Ans- D

Kudos [?]: 25 [2], given: 62

Senior Manager
Senior Manager
User avatar
G
Joined: 29 Jun 2017
Posts: 371

Kudos [?]: 70 [0], given: 66

GPA: 4
WE: Engineering (Transportation)
GMAT ToolKit User Reviews Badge
Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 04:07
@Buenel

My Answer is D here
just to prove D is correct and official answer is may be wrong.
first ring - 15:20
2nd 15:40
3rd 16:00
4th. 16:20
5th. 16:40
6. 17:00
7. 17:20
8. 17:40
9. 18:00
10. 18:20
11. 18:40
12th ring 19:00
Kudos for correct answer.
Also would like to mention i correctly answered https://gmatclub.com/forum/an-alarm-of- ... 44589.html question as well.
_________________

Give Kudos for correct answer and/or if you like the solution.

Kudos [?]: 70 [0], given: 66

Director
Director
avatar
P
Joined: 22 May 2016
Posts: 986

Kudos [?]: 342 [0], given: 593

Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 15:23
MathRevolution wrote:
An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30
B. 18:00
C. 18:30
D. 19:00
E. 19:30

MathRevolution , or Bunuel , or some moderator, would you please check the answer choices? I got D, and so did others who posted here.

I ran it twice more, using different methods. Still got Answer D.

Kudos [?]: 342 [0], given: 593

VP
VP
avatar
P
Joined: 26 Mar 2013
Posts: 1284

Kudos [?]: 296 [0], given: 165

Reviews Badge CAT Tests
Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 16 Aug 2017, 16:05
MathRevolution wrote:
An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30
B. 18:00
C. 18:30
D. 19:00
E. 19:30



the 12th ring = 15:20 + 1/3 * 11 = 15:20 + 3:40 = 19:00

Answer: D

Kudos [?]: 296 [0], given: 165

Intern
Intern
avatar
Joined: 18 Aug 2017
Posts: 2

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

Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 18 Aug 2017, 02:44
First alarm rings at 1520
Thus 12 alarm will ring in 11*20 =220 min
Thus 12th tym alarm will ring at 1520 + 3 hrs 40 min
Hence ans 1900 hrs
Ans D


Sent from my iPhone using GMAT Club Forum mobile app

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

Expert Post
Math Expert
User avatar
P
Joined: 02 Aug 2009
Posts: 5213

Kudos [?]: 5853 [0], given: 117

Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 18 Aug 2017, 03:36
MathRevolution wrote:
An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30
B. 18:00
C. 18:30
D. 19:00
E. 19:30



Hi..
If a clock rings at interval of 20 minutes and starts at 1520...
Ans has to be at _ _ 20, _ _ 40 or _ _ 60, can't be at _ _ 30

So answer given is clearly wrong ..

Now ans is 11*20+ 1520h..
11*20/60= 11/3= 3+2/3.. so 3 hours and 60*2/3=40 min.
So 15:20 + 3 hour and 30 mins=1900

D

Editing the OA
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 5853 [0], given: 117

Expert Post
Math Revolution GMAT Instructor
User avatar
P
Joined: 16 Aug 2015
Posts: 4326

Kudos [?]: 3041 [0], given: 0

GPA: 3.82
Premium Member CAT Tests
Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala [#permalink]

Show Tags

New post 20 Aug 2017, 18:25
=>The third alarm rings at 16:00, the sixth alarm rings at 17:00. Thus every third alarm rings every hour on the hour. The 12th alarm rings at 19:00.

Ans: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo

Kudos [?]: 3041 [0], given: 0

Re: An alarm of a certain clock rings every 20 minutes. If the clock's ala   [#permalink] 20 Aug 2017, 18:25
Display posts from previous: Sort by

An alarm of a certain clock rings every 20 minutes. If the clock's ala

  new topic 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®.