Melody

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Melody  11 feb 2022
 #4
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25 abr 2019
 #1
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It seems to me that this is going to be the same as rolling a dice 5 times and finding the probability that 4 is rolled any 2 times in a row.

call a 4 a success and any other a failure then   for any individual roll   P(S)=1/6     P(F)=5/6     

 

 

 

44444  Any 5 fours        1 way                                                   (1/6)^5

4444  any 4 fours           5 ways                                                 5*(1/6)^4*(5/6)

444      an 3 fours          5C3 ways = 10 ways                           10*(1/6)^3*(5/6)^2

except   4*4*4     no but all other 3 fours ok.    -1 way                (1/6)^3*(5/6)^2

No fours 1 way    (5/6)^5                                                               

P(4*4**)=P(4**4*)=P(4***4)=P(*4*4*)=P(*4**4)=P(**4*4) = (1/6)^2*(5/6)^3

 

 

\(\text {P(rolling 2 fours together in 5 rolls ) }\\ =\text{1-P(no fours)-P(1 four)-P(2 fours but not together) - P(3 fours but none together) } \\=1-(\frac{5}{6})^5- 5(\frac{1}{6})^1(\frac{5}{6})^4 - 6(\frac{1}{6})^2(\frac{5}{6})^3 - (\frac{1}{6})^3(\frac{5}{6})^2\)

 

1-(5/6)^5-5*(1/6)^1*(5/6)^4-6*(1/6)^2*(5/6)^3-(1/6)^3*(5/6)^2 = 0.0965792181069959   \(=\frac{751}{7776}\)

 

2 fours in the right places

44***

*44**

**44*

***44

P(2 fours in the right places) = 4*(1/6)^2(5/6)^3

 

OR

P(rolling 2 fours together)

=P(5 fours)+P(4 fours)+ P(3 fours) - P(4*4*4) +P(2 fours in the right places)

(1/6)^5+5*(1/6)^4*(5/6)^1+10*(1/6)^3*(5/6)^2-(1/6)^3*(5/6)^2+4*(1/6)^2(5/6)^3 = 0.0965792181069959    \(=\frac{751}{7776}\)

 

 

 

That is excellent.

I did it 2 different ways and got the same answer both times :)

24 abr 2019