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Praetorian
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MartinMag
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abhaypathania
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stolyar
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My versions:

(1) total outcomes 5^5; favorable outcomes are: fix one box as empty. The first ball has 4 boxes to be placed in, the second has 3, the third has 2, the fourth has 1, the fifth has 4. Each box can be fixed as empty.
Therefore, P = [4*3*2*1*4*5]/[5*5*5*5*5]= 0.1536

(2) four horses are losers and one is the winner.
P(to have W in any two)=1-P(LL)=1-4/5*3/4=2/5
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Vicky
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I go with Martin's answers:
1) 20/125 = 4/45
2) 2/5 ( = 4/5C2)
-vicky
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Ok, i was expecting someone to figure this out

Question : Are you all assuming that the marbles are distinguishable or otherwise...Does it matter if the marbles are distinguishable or not.

I mean if you can tell the difference between marbles, will the result be
any different.


make sense?

praetorian
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MartinMag
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It doesn't matter if the marbles are distinguishable or not, since all you want is your box to be empty.

In theory the ratio favorable outcomes to total outcomes would be unchanged.

Martin

PS: What was the answer by the way? Were Vicky and I correct?
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I go with Stoylar.. solutions...
1. i made a mistake in number of ways one can distribute 5 marbles in 4 boxes so that non is empty... 4*3*2*1*4*5....
there fore my answere would be : 0.15

2. The favourable outocome for in which there will be a winner always is 4
not 5 .. there fore we have : 4/ 5C2 = 2/5
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This is the official solution.

Number of ways to place 5 distinguishable balls in 5 distinguishable
boxes: 5^5 = 3125.

Number of boxes that can be empty: 5

Given an empty box, any one of the 4 remaining boxes can have 2
balls

There are 5C2 = 10 ways of placing two distinguishable balls in the
box allocated for 2 balls.

There are 3! = 6 ways of placing the three remaining balls in the 3
remaining boxes.

Total: 5*4*10*6 = 1200 ways of uniqely allocating 5 distinguishable
balls to 4 distinguisable boxes, leaving one box empty.

So the probability of exactly one box empty is 1200/3125 = 48/125.
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In the initial verbiage there is no info as to whether the balls are different. This info is crucial, but sometimes authors miss it making such a question be a pure nightmare. I wish I had not such a question on the test.



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