The last term is determined from probabilty laws: Since the Pr(one
person survives 30 years) = L60/L30, this implies that Pr(3 people
survive 30 years) = (L60/L30)^3. The Pr(one person surives at most 30
years) = Pr(one person dies within 30 years) = (L30 - L60)/L30. To get
the total probabiltiy that 3 people survive more than 30 yrs and one
person survives at most 30 years, you must mulitply these terms and then
mulitply by 4, because there are 4 different ways that you can "choose"
the combination of which of the 4 people will survive/not survive for 30
years.
Does anyone see this as incorrect?
> ----------
> From:
> Erica.Wheeler@uticanational.com[SMTP:Erica.Wheeler@uticanational.com]
> Sent: Thursday, August 27, 1998 7:58 AM
> To: studygroup4a@lists.casact.org
> Subject: Ch7 Parmenter
>
>
> I'm having a problem getting the answer for Chapter 7 - 4b.
>
> There are four people aged 30. Find the probability that at least 2
> of the
> people will survive for at most 30 years.
>
>
> Could someone explain to me how the answer in the back of the book is
> derived?
>
>
> Thanks.
> Erica
>