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stolyar
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GMAThopeful
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I would have to say 1/4.

The first ant can start in either direction. The other two ants will have to run in the same direction as the first ant so as not to collide.

P(the second ant runs in same dir as first)*P(the third ant runs in same dir as first)

Since each ant has 2 directions to run in, the Prob. would be:

1/2*1/2 = 1/4.
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mbagal1
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GMAThopeful


An after thought - this holds good only if the ants run with the same speed otherwise the ants will collide. :lol:


Yes, I also thought that we might need to add the prob. of the speeds, but looking at the answer choices decided that they were talking abt a "head-on" collision.
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techjanson
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stolyar
My friend claims this problem was offered during his interview with McKinsey.

There is a triangle, and there is an ant sitting on each vertex. All three ants start running simultaneously. What is the probability that they do not collide if they are running at the same speed?

A) 1/3
B) 2/3
C) 1/2
D) 1/4
E) 1/8


There are 8 ways (directions) on which each ant can run. Out of these only 2 wont result in collision hence P is 2/8 or 1/4



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