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Two objects are placed on opposite corners of a cube. The [#permalink]
15 Jan 2008, 11:35

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56% (04:25) correct
44% (02:13) wrong based on 7 sessions

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?

Re: PS: Probability [#permalink]
15 Jan 2008, 12:24

Expert's post

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. _________________

Re: PS: Probability [#permalink]
15 Jan 2008, 19:36

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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.

Re: PS: Probability [#permalink]
16 Jan 2008, 04:21

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Expert's post

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} _________________

Re: PS: Probability [#permalink]
27 Sep 2009, 05:42

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 =

Re: PS: Probability [#permalink]
14 Feb 2010, 13:31

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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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Re: PS: Probability [#permalink]
17 Aug 2010, 01:38

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

************************ Kudos to me if you like this post!

Re: PS: Probability [#permalink]
26 Sep 2010, 06:04

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.

Re: PS: Probability [#permalink]
14 Oct 2010, 07:38

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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

Re: PS: Probability [#permalink]
10 Apr 2011, 06:52

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

Re: Two objects are placed on opposite corners of a cube. The [#permalink]
25 Feb 2012, 18:10

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%

gmatclubot

Re: Two objects are placed on opposite corners of a cube. The
[#permalink]
25 Feb 2012, 18:10