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At exactly what time past 7:00 will the minute and hour [#permalink]
11 Jul 2003, 18:41

4

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

85% (hard)

Question Stats:

46% (03:11) correct
54% (02:33) wrong based on 45 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

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

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

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.

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

Re: At exactly what time past 7:00 will the minute and hour [#permalink]
03 Sep 2014, 12:33

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 minute 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".

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Re: At exactly what time past 7:00 will the minute and hour
[#permalink]
03 Sep 2014, 12:33

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