Probability he was 'done in' by chocolate mousse

Tascja

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Mar 4, 2006
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I'm doing my probability assignment and I having trouble understanding which type of probability formula I will need to use to solve this question:

Bart is planning to murder his rich Uncle Basil in hopes of claiming his inheritance a bit early. Hoping to take advantage of his uncle's predilection for immoderate desserts, Bart has put rat poison in the cherries flambe and cyanide in the chocolate mousse. The probability of the rat poison being fatal is 60 percent; the cyanide 90 percent. Bart estimates that Basil has a 60 percent chance of ordering the cherries and a 40 percent chance of ordering the mousse. Given that Basil did, indeed, suffer a premature demise, what is the probability that he was done in by the chocolate mousse?

Do you think that you have to multiply the chance that he will pick the chocolate mousse by the probability that he wont pick the cherries, then multiply it by the prob that he will die from the mousse??
 
Re: Probability of picking one

Not exactly a socially acceptable problem, is it?

Cherries, 60%, Rat Poison, 60%
Mousse, 40%, Cyanide, 90%

The entire distribution, then, is

Order Cherries and Live: 0.60*0.40 = 0.24
Order Cherries and Die: 0.60*0.60 = 0.36
Order Mousse and Live: 0.40*0.10 = 0.04
Order Mousse and Die: 0.40*0.90 = 0.36

Checking: 0.24+0.36+0.04+0.36 = 1.00 -- Good.

He's no longer with us:

Order Cherries and Die: 0.60*0.60 = 0.36
Order Mousse and Die: 0.40*0.90 = 0.36

0.36+0.36 = 0.72

Can you now answer the question?
 
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