Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 43892

A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
21 Feb 2014, 00:10
Question Stats:
53% (01:40) correct 47% (01:40) wrong based on 726 sessions
HideShow timer Statistics
The Official Guide For GMAT® Quantitative Review, 2ND EditionA certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke? (A) 72 (B) 50 (C) 48 (D) 46 (E) 44 Problem Solving Question: 110 Category: Arithmetic Operations on rational numbers Page: 75 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you!
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
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? Extrahard Quant Tests with Brilliant Analytics



Math Expert
Joined: 02 Sep 2009
Posts: 43892

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
21 Feb 2014, 00:10
4
This post received KUDOS
Expert's post
6
This post was BOOKMARKED



Intern
Status: Never Give up!!!
Joined: 02 Aug 2012
Posts: 49
Location: India
Concentration: Finance, General Management

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
21 Feb 2014, 01:03
9
This post received KUDOS
4
This post was BOOKMARKED
Very easy question once you figure out the meaning of  'by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes'
What this means is that if it is 6 O Clock  then the clock will strike 6 times with 5 intervals in between those 6 strikes each interval time = to the time of each strike. Which basically means 11 same time gaps as seen below: Strike 1>interval time 1>Strike 2>Interval time 2>Strike 3>.....Interval time 5>Strike 6.
The question says that at 6 O Clock the time between begining of first stroke and end of last stroke = 22secs since all time intervals and strike times are same total no of strikes+time intervals = 11 Time per strike = Time per interval = 22/11 = 2secs
Now at 12 O Clock there will be 12 strikes and 11 intervals, since each has the same time (2secs) the time elapsed from the begining of the first stroke to the end of the last stroke = (12+11)x2 = 46 seconds
Option (D)



Math Expert
Joined: 02 Sep 2009
Posts: 43892

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
22 Feb 2014, 05:36
1
This post received KUDOS
Expert's post
2
This post was BOOKMARKED



SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1839
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
13 Mar 2014, 22:05
For 6:00 clock there, time elapsed = 22 seconds So, to stroke 6, 5 empty time slots would be required Total = 6 + 5 = 11 slots So one slot will require = 22/11 = 2 seconds. We can also generalize this information by putting in a formula: For n time, it will be n + n1 = (2n1) Time elapsed between First & Last Stroke = (2n1) x 2 where n = Time displayed So for 12'o clock, it would be (241) x 2 = 46 = Answer = D Bunuel, can you please tell if this approach is correct.
_________________
Kindly press "+1 Kudos" to appreciate



Manager
Joined: 11 Sep 2013
Posts: 158
Concentration: Finance, Finance

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
17 Oct 2014, 10:00
Hi, Bunuel If I change the question little bit what will be the answer?
A certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly twice the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke?



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11066
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
09 Dec 2015, 11:30
Hi Raihanuddin, I'm not sure if you're still interested in this post (since it's from over a year ago), but here is the answer to your question: The change that you've made to the prompt will lead to an answer that is NOT an integer, but here's how you would go about solving it. By making the interval between strokes TWICE the length of a single stroke, and keeping the fact that at 6:00 we have 22 seconds from the start of the first stroke to the end of the last stroke.... We have.... 6 strokes x seconds per stroke 5 intervals @ 2X seconds per interval 6(X) + 5(2X) = 16X seconds 16X = 22 seconds X = 22/16 = 11/8 seconds So at 12:00, we have... 12 strokes x seconds per stroke 11 intervals @ 2X seconds per interval 12(X) + 11(2X) = 34X seconds Plugging in the value of X, we have.... 34(11/8) = 17(11/4) = 187/4 seconds = 46 3/4 seconds GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************



Manager
Joined: 23 Dec 2013
Posts: 235
Location: United States (CA)
GMAT 1: 710 Q45 V41 GMAT 2: 760 Q49 V44
GPA: 3.76

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
25 May 2017, 18:42
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionA certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke? (A) 72 (B) 50 (C) 48 (D) 46 (E) 44 Problem Solving Question: 110 Category: Arithmetic Operations on rational numbers Page: 75 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you! There are 6 clock strikes and 5 intervals between strikes. 6+5 = 11 periods throughout the 22 seconds. 22/11 = 2 seconds/period. At 12:00, there will be 12 clock strikes and 11 intervals 23*2 = 46 seconds total.



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2016

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
31 May 2017, 18:11
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionA certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke? (A) 72 (B) 50 (C) 48 (D) 46 (E) 44 We are given that a certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes. Since at 6:00 the lapse between the beginning and the last stroke is 22 seconds, we can create the following equation in which x = the time between strokes = the time for each stroke. Since there are 6 strikes at 6:00, we have: strike  lapse  strike  lapse  strike  lapse  strike  lapse  strike  lapse  strike There are 6 strikes and 5 lapses, and thus: 6x + 5x = 22 11x = 22 x = 2 seconds So, at 12:00 there will be 12 strikes and 11 lapses. Thus, the total time will be: 12(2) + 11(2) = 24 +22 = 46 seconds. Answer: D
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



SVP
Joined: 11 Sep 2015
Posts: 2065
Location: Canada

Re: A certain clock marks every hour by striking a number of tim [#permalink]
Show Tags
31 Jan 2018, 07:16
1
This post received KUDOS
Expert's post
1
This post was BOOKMARKED
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionA certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke? (A) 72 (B) 50 (C) 48 (D) 46 (E) 44 In some regards, this is more of a Reading Comprehension question than a Quantitative question ... the time required FOR a stroke is exactly equal to the time interval BETWEEN strokes.So, we have moments of silence and moments where the clock is ringing. Each period of silence is the same duration as each period of noise. So, for example, at 3:00, we have ( RING)( silence)( RING)( silence)( RING) At 6:00 the time lapse between the beginning of the first stoke and the end of the last stroke is 22 secondsSo, at 6:00, we have ( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING) Notice that, if we count RINGS and silences, we have a total of 11 periods. If the entire event takes 22 seconds, we can conclude that each period is 2 seconds long. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke? We can conclude that this event will include 12 RINGS and 11 silences for a total of 23 periods. Since each each period is 2 seconds long, the entire event will take 46 seconds Answer: D Aside: If you're not convinced that there will be 12 RINGS and 11 silences, you can always write it out . .. At 12:00, we have ( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING)( silence)( RING) Cheers, Brent
_________________
Brent Hanneson – Founder of gmatprepnow.com




Re: A certain clock marks every hour by striking a number of tim
[#permalink]
31 Jan 2018, 07:16






