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# Two objects are placed on opposite corners of a cube. The

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Senior Manager
Joined: 22 Sep 2005
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Two objects are placed on opposite corners of a cube. The  [#permalink]

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15 Jan 2008, 12:35
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67% (02:38) correct 33% (02:13) wrong based on 33 sessions

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Two objects are placed on opposite corners of a cube. The objects are designed only to move along the edges of the cube and are equipped with a power device which allows them to do so at the same constant speed of S inches per minute. If both objects begin moving at the same time, each taking one of the shortest paths towards the initial position of the other, what is the probability that the two objects will collide?
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15 Jan 2008, 13:24
1/36

Each object should pass trough 3 consecutive edges. Two objects can collide at the middle point of second edge in paths. There are exactly 6 middle points for a cube. Therefore, the probability is 1/6*1/6=1/36

a good question (+1) but it seems be out of GMAT.
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15 Jan 2008, 20:36
2
netcaesar wrote:
Two objects are placed on opposite corners of a cube. The objects are designed only to move along the edges of the cube and are equipped with a power device which allows them to do so at the same constant speed of S inches per minute. If both objects begin moving at the same time, each taking one of the shortest paths towards the initial position of the other, what is the probability that the two objects will collide?

From 2 opposite corners of a cube, there are 6 shortest routes connecting each other (along 3 edges). Out of these 6, if the same path is chosen by the 2 objects then collision will result at the center of 2 edge. So probability is 1/6.
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15 Jan 2008, 21:41
rgajare14 wrote:
So probability is 1/6.

You are right. I forgot to multiply by 6 in my approach. Answer is 1/6.
+1
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Updated on: 16 Jan 2008, 06:45
1
kazakhb wrote:
why should we multiply by 6?

we have 6 points.
the total number of different combinations is 6(first object)*6(second object)=36
the number of combinations with collision is 6 (not 1 as I thought)
Therefore,
$$p = \frac{6}{36} = \frac{1}{6}$$
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Originally posted by walker on 16 Jan 2008, 05:21.
Last edited by walker on 16 Jan 2008, 06:45, edited 1 time in total.
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25 Aug 2008, 05:40
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1
You need minimum of 3 steps to get to the opposite corners. 1 step along x,y,and z axis each. The total number of routes is
3!/(1!*1!*1!) = 6.

The other guy has 6 routes too.
If others' route is fixed, then 1/6 of your routes will lead to collision.

so p=1/6
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27 Sep 2009, 06:42
Two objects are placed on opposite corners of a cube. The objects are designed only to move along the edges of the cube and are equipped with a power device which allows them to do so at the same constant speed of S inches per minute. If both objects begin moving at the same time, each taking one of the shortest paths towards the initial position of the other, what is the probability that the two objects will collide?

Ans: Each object has 6 ways to reach the other object's initial position. (passing through 3 connected edges)
Hence total number of possibilities = 6 * 6 = 36

Of these 36 ways , collision will occur if each object chooses the same path, i.e both should follow one of the possible 6 ways
= 6
Probability that they will collide = 6/36 = 1/6
=
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14 Feb 2010, 14:31
1
netcaesar wrote:
Two objects are placed on opposite corners of a cube. The objects are designed only to move along the edges of the cube and are equipped with a power device which allows them to do so at the same constant speed of S inches per minute. If both objects begin moving at the same time, each taking one of the shortest paths towards the initial position of the other, what is the probability that the two objects will collide?

We need the possible short paths from the opposite corners.

The object would need to travel 2 times horizontal and once vertical to reach the opposite corner via the shortest path. Hence total number of paths = 3! (arrange HHV in diff comb).

The probability of collision can be if both the objects take the same path. Therefore = 1 / 3! = 1/6
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17 Aug 2010, 02:38
Two objects are placed on opposite corners of a cube. The objects are designed only to move along the edges of the cube and are equipped with a power device which allows them to do so at the same constant speed of S inches per minute. If both objects begin moving at the same time, each taking one of the shortest paths towards the initial position of the other, what is the probability that the two objects will collide?

Tell me if this is the right method too. This method that I took seemed simpler when compared.

There are 6 shortest ways to travel to the opposite corner of the cube.
First object can take route in 6/6 ways.

If the second object has to collide into this, it has to choose the one route that the first object has chosen. So in 1/6 ways.

Therefore total probability = (6/6)*(1/6) = 1/6

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26 Sep 2010, 07:04
I used the following approach, though don't no is it right.
Any object has to go 3 points to reach the opposite corner.
The total number of ways is 3*2*1=6.
Hence, two objects will collide if they chose the same route and the chance is 1/6.
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26 Sep 2010, 21:52
good question ... the ans is 1/6..

the number of possible ways to reach to other end for object A = 6
the number of possible ways to reach to other end for object B = 6

so the probability of meeting each other = (1/6)(1/6)=1/36

the number of possible start point =6

so the probability is 6/36 = 1/6
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14 Oct 2010, 08:38
My ans is 1/6..bt i solved in another way...
there are 6 ways by which any object move from one end to its opp end(shortest way)..
and if both object has to collide thn they will move on same way..means there is only one way..
so prob is 1/6
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10 Apr 2011, 07:52
My Solution:

So object 1 has 3 steps to go to object 2's initial position. Object one can choose from among 3 edges, from that from two edges then with 1 edge so 3 x 2 x 1 = 6. Object 2 has the same 6 possible routes.

6 x 6 = 36 all possible comb. routes of object 1 and 2

For them to collide, 6 ways for them to collide.

6/36 = 1/6

I find this one tough
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Re: Two objects are placed on opposite corners of a cube. The  [#permalink]

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25 Feb 2012, 19:10
1
There are six possible paths:

The first object's path could be picked in 6 ways: 6/6
The second object's path needs to pick the same path: 1/6
Probability that they're both on the same path: 6/6 * 1/6
= 1/6 = 16.67%
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Re: Two objects are placed on opposite corners of a cube. The  [#permalink]

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12 Dec 2017, 21:14
Say, from opposite corner A, we can reach diagonally opposite corner B, with three hops -> 1 along (x direction), 1 along (y direction), 1 along (z direction) => total ways to reach = permutation of (x,y,z) = 3! = 6

Likewise, from opposite corner B, we can reach diagonally opposite corner A, with three hop => total ways = 3! = 6

So total ways for each point to reach each other's initial point = 6 * 6 = 36

out of this, if out of 6 ways, say A, takes x->z->y and then point B, must take y->z->x to collide.

So for each one of 6 ways, point A will take, point B must take one of its 6 ways to collide => total favourable = 6

Required probability = 6/36 = 1/6
Re: Two objects are placed on opposite corners of a cube. The &nbs [#permalink] 12 Dec 2017, 21:14
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