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 #3
avatar+98 
+1
Feb 13, 2019
 #2
avatar+26376 
+7

An ant moves on the following lattice, beginning at the dot labeled A.
Each minute he moves to one of the dots neighboring the dot he was at, choosing from among its neighbors at random.
What is the probability that after 5 minutes he is at the dot labeled B ?

 

My attempt:

\(\begin{array}{|r|r|r|} \hline & \text{path} & \text{probability} & \text{probability} \\ \hline 1& 3,2,3,2,3,&0.0039062500 \\ 2& 3,2,3,4,3,&0.0039062500\\ 3& 3,2,3,7,3,&0.0019531250\\ 4& 3,2,3,1,3,&0.0078125000 \\ 5& 3,2,6,2,3,&0.0039062500 \\ 6& 3,2,6,7,3,&0.0019531250 \\ 7& 3,4,3,2,3,&0.0039062500 \\ 8& 3,4,3,4,3,&0.0039062500 \\ 9& 3,4,3,7,3,&0.0019531250 \\ 10& 3,4,3,1,3,&0.0078125000 \\ 11& 3,4,8,4,3,&0.0039062500 \\ 12& 3,4,8,7,3,&0.0019531250 \\ 13& 3,7,3,2,3,&0.0019531250 \\ 14& 3,7,3,4,3,&0.0019531250 \\ 15& 3,7,3,7,3,&0.0009765625 \\ 16& 3,7,3,1,3,&0.0039062500 \\ 17& 3,7,6,2,3,&0.0019531250 \\ 18& 3,7,6,7,3,&0.0009765625 \\ 19& 3,7,8,4,3,&0.0019531250 \\ 20& 3,7,8,7,3,&0.0009765625 \\ 21& 3,7,11,7,3,&0.0009765625 \\ 22& 3,1,3,2,3,&0.0078125000 \\ 23& 3,1,3,4,3,&0.0078125000 \\ 24& 3,1,3,7,3,&0.0039062500 \\ 25& 3,1,3,1,3,&0.0156250000 \\ 26& 6,2,3,2,3,&0.0039062500 \\ 27& 6,2,3,4,3,&0.0039062500 \\ 28& 6,2,3,7,3,&0.0019531250 \\ 29& 6,2,3,1,3,&0.0078125000 \\ 30& 6,2,6,2,3,&0.0039062500 \\ 31& 6,2,6,7,3,&0.0019531250 \\ 32& 6,5,6,2,3,&0.0078125000 \\ 33& 6,5,6,7,3,&0.0039062500 \\ 34& 6,7,3,2,3,&0.0019531250 \\ 35& 6,7,3,4,3,&0.0019531250 \\ 36& 6,7,3,7,3,&0.0009765625 \\ 37& 6,7,3,1,3,&0.0039062500 \\ 38& 6,7,6,2,3,&0.0019531250 \\ 39& 6,7,6,7,3,&0.0009765625 \\ 40& 6,7,8,4,3,&0.0019531250 \\ 41& 6,7,8,7,3,&0.0009765625 \\ 42& 6,7,11,7,3,&0.0009765625 \\ 43& 6,10,6,2,3,&0.0039062500 \\ 44& 6,10,6,7,3,&0.0019531250 \\ 45& 6,10,11,7,3,&0.0019531250 \\ 46& 8,4,3,2,3,&0.0039062500 \\ 47& 8,4,3,4,3,&0.0039062500 \\ 48& 8,4,3,7,3,&0.0019531250 \\ 49& 8,4,3,1,3,&0.0078125000 \\ 50& 8,4,8,4,3,&0.0039062500 \\ 51& 8,4,8,7,3,&0.0019531250 \\ 52& 8,7,3,2,3,&0.0019531250 \\ 53& 8,7,3,4,3,&0.0019531250 \\ 54& 8,7,3,7,3,&0.0009765625 \\ 55& 8,7,3,1,3,&0.0039062500 \\ 56& 8,7,6,2,3,&0.0019531250 \\ 57& 8,7,6,7,3,&0.0009765625 \\ 58& 8,7,8,4,3,&0.0019531250 \\ 59& 8,7,8,7,3,&0.0009765625 \\ 60& 8,7,11,7,3,&0.0009765625 \\ 61& 8,9,8,4,3,&0.0078125000 \\ 62& 8,9,8,7,3,&0.0039062500 \\ 63& 8,12,8,4,3,&0.0039062500 \\ 64& 8,12,8,7,3,&0.0019531250 \\ 65& 8,12,11,7,3,&0.0019531250 \\ 66& 11,7,3,2,3,&0.0019531250 \\ 67& 11,7,3,4,3,&0.0019531250 \\ 68& 11,7,3,7,3,&0.0009765625 \\ 69& 11,7,3,1,3,&0.0039062500 \\ 70& 11,7,6,2,3,&0.0019531250 \\ 71& 11,7,6,7,3,&0.0009765625 \\ 72& 11,7,8,4,3,&0.0019531250 \\ 73& 11,7,8,7,3,&0.0009765625 \\ 74& 11,7,11,7,3,&0.0009765625 \\ 75& 11,10,6,2,3,&0.0039062500 \\ 76& 11,10,6,7,3,&0.0019531250 \\ 77& 11,10,11,7,3,&0.0019531250 \\ 78& 11,12,8,4,3,&0.0039062500 \\ 79& 11,12,8,7,3,&0.0019531250 \\ 80& 11,12,11,7,3,&0.0019531250 \\ 81& 11,13,11,7,3,&0.0039062500& \text{sum } = 0.2500000000 \\ \hline \end{array}\)

 

The probability that after 5 minutes he is at the dot labeled B is \(0.25\ (25\ \%)\)

 

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Feb 13, 2019
 #1
avatar+36919 
0
Feb 13, 2019
 #2
avatar+36919 
0
Feb 13, 2019

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