Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 23 May 2015, 07:19

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# At exactly what time past 7:00 will the minute and hour

Author Message
TAGS:
GMAT Instructor
Joined: 07 Jul 2003
Posts: 770
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
Followers: 13

Kudos [?]: 56 [1] , given: 0

At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 18:41
1
KUDOS
6
This post was
BOOKMARKED
00:00

Difficulty:

75% (hard)

Question Stats:

57% (03:18) correct 43% (03:19) wrong based on 133 sessions
At exactly what time past 7:00 will the minute and hour hands of an accurate working clock be precisely perpendicular to each other for the first time?

(A) 20 13/21 minutes past 7:00
(B) 20 13/17 minutes past 7:00
(C) 21 3/23 minutes past 7:00
(D) 21 9/11 minutes past 7:00
(E) 22 4/9 minutes past 7:00
[Reveal] Spoiler: OA

_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Director
Joined: 03 Jul 2003
Posts: 655
Followers: 2

Kudos [?]: 26 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 20:54
Is it D? My Guesstimate after spending 21 minutes !
Hope GMAT is not this tough
GMAT Instructor
Joined: 07 Jul 2003
Posts: 770
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
Followers: 13

Kudos [?]: 56 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 21:06
Sorry. Guessing not allowed. Show me how you solved it.

(It is NOT that hard if you take the right approach).

Motto: Spoonfed knowledge is not well retained, but knowledge worked hard for will be cherished for a long time....
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Director
Joined: 03 Jul 2003
Posts: 655
Followers: 2

Kudos [?]: 26 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 22:36
Dear AkamaiBrah,

Thank you for not only posting such a nice questions, but also soving
the tough ones. Wish I had a teahcer like you when I was in school.

Here is my ans: D

A1 = hour angle
A2 = minute angle
A1-A2 = 90
Assume the minutes = M
A1 = (7*60+M)/12*60 )*360
A2 = M*360/60

Solving all three equation , results in the answer D
Director
Joined: 03 Jul 2003
Posts: 655
Followers: 2

Kudos [?]: 26 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 22:38
BTW:

Which one is correct? "Such a nice questions" or "Such nice questions" or "Such a nice question"
Manager
Joined: 28 Feb 2003
Posts: 100
Followers: 1

Kudos [?]: 3 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  11 Jul 2003, 23:04
210 + M/12 - M = 90

Let M be the degrees covered by minute hand from zero. (7:00 pm is the reference point)
initially difference is 210 deg. Hour hand will move at the rate of M/12, so after M minutes hour hand will be at 210+M/12 and minute hand will be at M. The difference should be 90. Find M and divide by 6, which will give you the minutes.

Manager
Joined: 08 Apr 2003
Posts: 149
Followers: 1

Kudos [?]: 9 [4] , given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  12 Jul 2003, 03:56
4
KUDOS
4
This post was
BOOKMARKED
OKies my idea of solution,

I found it the fastest way,

Speed of hour hand/min = 360/12*60 = 1/2.

Speed of minuted hand/min = 360/60 = 6.

Relative speed = 11/2 degrees/min

Now at 7 the two are 210 degrees apart.
From 210 degress to 90 degrees. Minute has to gain 120 over the hour hand.

So time required will be = 120/Relative speed = 120*2/11 = 21 9/11 = D
GMAT Instructor
Joined: 07 Jul 2003
Posts: 770
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
Followers: 13

Kudos [?]: 56 [0], given: 0

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  12 Jul 2003, 07:49
The answer is D. Evensflow did it the fastest although all of the solutions were fine. The key is computing the rate of each hand and solving for when they are 90 deg apart.

Good job all.
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Verbal Forum Moderator
Status: After a long voyage, land is visible.
Joined: 22 Mar 2013
Posts: 989
Location: India
GPA: 3.51
WE: Information Technology (Computer Software)
Followers: 88

Kudos [?]: 642 [3] , given: 222

At exactly what time past 7:00 will the minute and hour [#permalink]  03 Sep 2014, 12:33
3
KUDOS
2
This post was
BOOKMARKED
At 7:00, minute hand must be at 210 degree from 12 (clock wise).
Minute hand of the clock moves with 6 degree per minute speed and hour hand moves at 1/2 degree per minute.
Therefore in x min hour hand will travel (1/2)*x degree further 210 degree from initial position; meanwhile minute hand must cover 6x degrees. Difference between minute and hour hand is required 90 degree. Formed following equation and solved for x.

$$(\frac{1}{2}x + 210) - 6x = 90$$
Solve: x=240/11

Ans D.
_________________

Piyush K
-----------------------
Our greatest weakness lies in giving up. The most certain way to succeed is to try just one more time. ― Thomas A. Edison
Don't forget to press--> Kudos
My Articles: 1. WOULD: when to use? | 2. All GMATPrep RCs (New)
Tip: Before exam a week earlier don't forget to exhaust all gmatprep problems specially for "sentence correction".

Intern
Joined: 06 Jun 2014
Posts: 26
Followers: 0

Kudos [?]: 1 [0], given: 52

At exactly what time past 7:00 will the minute and hour [#permalink]  12 May 2015, 13:02
Anotehr way to solve this problem is to use the formula that we have for the angle of the clock needels.

$$angle of clock needels =\frac{(60H + 11M)}{2}$$ where H is the hour and the M is the minutes.
We can imply that the H= 7 because the strating point is 7:00 any way and just need to find the M in the equation with making teh equation equal to 90 since that is what is being asked.
Do the math and you will see that $$M=21\frac{9}{11}$$

So not bad to learn the formula at beggiging I was struguling with teh question and trying to go figure out some other stuff, but than I remmeberd on this formula and applied it.

hope it helps
Intern
Joined: 18 May 2014
Posts: 31
Followers: 1

Kudos [?]: 3 [0], given: 140

Re: At exactly what time past 7:00 will the minute and hour [#permalink]  20 May 2015, 19:10
PiyushK wrote:
At 7:00, minute hand must be at 210 degree from 12 (clock wise).
Minute hand of the clock moves with 6 degree per minute speed and hour hand moves at 1/2 degree per minute.
Therefore in x min hour hand will travel (1/2)*x degree further 210 degree from initial position; meanwhile minute hand must cover 6x degrees. Difference between minute and hour hand is required 90 degree. Formed following equation and solved for x.

$$(\frac{1}{2}x + 210) - 6x = 90$$
Solve: x=240/11

Ans D.

Thanks for the solution. This cleared up the confusions I had in my head, bigtime!
Re: At exactly what time past 7:00 will the minute and hour   [#permalink] 20 May 2015, 19:10
Similar topics Replies Last post
Similar
Topics:
If a car traveled for 2 hours from 7:00 till 9:00 (m25#5) 1 15 Feb 2012, 05:41
9 There are how many hours between x minutes past 12 noon and 6 09 Jun 2009, 19:24
1 What is the angle between the minute and the hour hand of 7 15 May 2008, 21:00
What is the angle between the minute and the hour hands of 1 18 Feb 2007, 01:15
what is the angle between the minute and hour hand of the 2 15 Nov 2006, 05:21
Display posts from previous: Sort by