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

It is currently 24 Aug 2019, 00:02

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

A searchlight on top of the watch-tower makes 3 revolutions

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

Hide Tags

Find Similar Topics 
Intern
Intern
avatar
Joined: 09 Sep 2014
Posts: 6
A searchlight on top of the watch-tower makes 3 revolutions  [#permalink]

Show Tags

New post 08 Oct 2014, 16:29
A very literal solution...


One minute <-------------|---------------|---------------->
************************** 14-24 **********36-44*************

Segment at which darkness will intercede 5 seconds

Time between 15+9+15 = 13/20

& Closest answer is 3/4.....
Intern
Intern
avatar
B
Joined: 02 Dec 2017
Posts: 2
Re: A searchlight on top of the watch-tower makes 3 revolutions  [#permalink]

Show Tags

New post 04 Feb 2018, 08:35
I approached this question as if the length of a minute is the length of a rope. Let's say we have a length of a rope-60cm. And every 20cm, there is a cut.
--------20--------20--------20
-----15-20-----15-20------15-20
Probability of man being in every 15 cm or less is calculated as follows. Overall there are 5+5+5 areas that the man should not stand, if it wants to be waiting at least 5 seconds (which are the areas between 15 and 20, 35 and 40, 55 and 60). Overall, 5+5+5=15. P=1- 15/60=3/4
VP
VP
User avatar
P
Joined: 03 Jun 2019
Posts: 1056
Location: India
Re: A searchlight on top of the watch-tower makes 3 revolutions  [#permalink]

Show Tags

New post 21 Jul 2019, 22:18
marcodonzelli wrote:
A searchlight on top of the watch-tower makes 3 revolutions per minute. What is the probability that a man appearing near the tower will stay in the dark for at least 5 seconds?

(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) 3/4


One revolutions = 60 seconds / 3 revolutions = 20 seconds / revolutions
Probability that a man will stay in dark for max 5 seconds =5/20 =1/5
probability that a man appearing near the tower will stay in the dark for at least 5 seconds = 1-1/4 = 3/4

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
Intern
Intern
avatar
B
Joined: 02 Mar 2019
Posts: 5
Re: A searchlight on top of the watch-tower makes 3 revolutions  [#permalink]

Show Tags

New post 22 Jul 2019, 01:16
Isn't it .. probability of staying in dark in from starting point to 5sec is ..1/20 + 2/20 + 3/20 + 4/20 + 5/20 = 3/4

Posted from my mobile device
GMAT Club Bot
Re: A searchlight on top of the watch-tower makes 3 revolutions   [#permalink] 22 Jul 2019, 01:16

Go to page   Previous    1   2   [ 24 posts ] 

Display posts from previous: Sort by

A searchlight on top of the watch-tower makes 3 revolutions

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





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