- #1

succubus

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The question:

A family has j children with probability p1 = .1, p2 = .25, p3 = .35, p4 = .3.

A child is randomly chosen. Given this child is the eldest in the family, find the conditional probability that

a) Family has 1 child

b) Family has 4 children

A is easy (1), so let's move to b.

I have the following setup

E = event child is eldest

F = event family has 4 children

P(E) = (1*.1) + (.5 * .25) + (.3333 * .35) + (.25 * .3)

And

P(F) = .3

So the set up should be P(F|E) = .25*P(E)/P(E) ??

The events are independent correct? So I probably shouldn't include the ratio of how many children there are to choose from multiplied by the probability??

I'm kind of anxious and worried. Got 3 tests to study for an am sick. So I apologize if it's too easy :)