Hi I really need some better explanation for this, not answered well anywhere!
Gmat prep problem  Expert's help preferred
This topic has expert replies

 Master  Next Rank: 500 Posts
 Posts: 370
 Joined: 11 Jun 2011
 Location: Arlington, MA.
 Thanked: 27 times
 Followed by:2 members
 GMATGuruNY
 GMAT Instructor
 Posts: 15533
 Joined: 25 May 2010
 Location: New York, NY
 Thanked: 13060 times
 Followed by:1898 members
 GMAT Score:790
Each time the ball descends a level, it has 2 options: to fall TO THE LEFT or TO THE RIGHT.
Since the ball descends 3 levels, and there are 2 options for each level, the total number of routes = 2*2*2 = 8.
There is only 1 way to land in slot 1 (straight down the left side of the triangle) and only 1 way to land in slot 4 (straight down the right side of the triangle).
Each of the 6 remaining routes leads to the one of the two middle slots.
Since the probability of landing in either of the two middle slots is the same, 3 of these 6 remaining routes lead to slot 2.
Thus, P(slot 2) = 3/8.
The correct answer is D.
Since the ball descends 3 levels, and there are 2 options for each level, the total number of routes = 2*2*2 = 8.
There is only 1 way to land in slot 1 (straight down the left side of the triangle) and only 1 way to land in slot 4 (straight down the right side of the triangle).
Each of the 6 remaining routes leads to the one of the two middle slots.
Since the probability of landing in either of the two middle slots is the same, 3 of these 6 remaining routes lead to slot 2.
Thus, P(slot 2) = 3/8.
The correct answer is D.
Mitch Hunt
Private Tutor for the GMAT and GRE
[email protected]
If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon.
Available for tutoring in NYC and longdistance.
For more information, please email me at [email protected].
Student Review #1
Student Review #2
Student Review #3
Private Tutor for the GMAT and GRE
[email protected]
If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon.
Available for tutoring in NYC and longdistance.
For more information, please email me at [email protected].
Student Review #1
Student Review #2
Student Review #3

 Master  Next Rank: 500 Posts
 Posts: 370
 Joined: 11 Jun 2011
 Location: Arlington, MA.
 Thanked: 27 times
 Followed by:2 members

 Master  Next Rank: 500 Posts
 Posts: 242
 Joined: 01 Aug 2008
 Location: Delhi
 Thanked: 6 times
[quote="GMATGuruNY"]Each time the ball descends a level, it has 2 options: to fall TO THE LEFT or TO THE RIGHT.
Since the ball descends 3 levels, and there are 2 options for each level, the total number of routes = 2*2*2 = 8.
[color=red]There is only 1 way to land in slot 1 (straight down the left side of the triangle) and only 1 way to land in slot 4 (straight down the right side of the triangle).
Each of the 6 remaining routes leads to the one of the two middle slots.[/color]
Since the probability of landing in either of the two middle slots is the same, 3 of these 6 remaining routes lead to slot 2.
Thus, P(slot 2) = 3/8.
The correct answer is [spoiler]D[/spoiler].[/quote]
Please explain the red coloured portion as I could not understand it.
Since the ball descends 3 levels, and there are 2 options for each level, the total number of routes = 2*2*2 = 8.
[color=red]There is only 1 way to land in slot 1 (straight down the left side of the triangle) and only 1 way to land in slot 4 (straight down the right side of the triangle).
Each of the 6 remaining routes leads to the one of the two middle slots.[/color]
Since the probability of landing in either of the two middle slots is the same, 3 of these 6 remaining routes lead to slot 2.
Thus, P(slot 2) = 3/8.
The correct answer is [spoiler]D[/spoiler].[/quote]
Please explain the red coloured portion as I could not understand it.

 Senior  Next Rank: 100 Posts
 Posts: 57
 Joined: 21 Dec 2009
 Location: Melbourne, Australia
 Thanked: 17 times
 sam2304
 Legendary Member
 Posts: 1239
 Joined: 26 Apr 2011
 Thanked: 233 times
 Followed by:26 members
 GMAT Score:680
To hit cell numbered 1, the ball has to come all the way left, if it goes right anywhere in the middle it won't hit cell 1. So there is only 1 way. [see the picture if you don't understand it] Similar manner to hit 4 it has to go all the way right  one way. Total 8 ways, one for cell 1, one for cell 4 and remaining 6 for cell 2 and 3.There is only 1 way to land in slot 1 (straight down the left side of the triangle) and only 1 way to land in slot 4 (straight down the right side of the triangle).
Each of the 6 remaining routes leads to the one of the two middle slots.
Please explain the red coloured portion as I could not understand it.
Getting defeated is just a temporary notion, giving it up is what makes it permanent.
https://gmatandbeyond.blogspot.in/
https://gmatandbeyond.blogspot.in/