what is the expected payment? mathematical expectation

sunny1324

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Joined
Jul 12, 2008
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The problem is:

Let the random variable X be the number of days that a certain patient needs to be in the hospital. Say X has the p.m.f. of (5-x)/10 where x=1,2,3,4

if the patient is to receive from an insurance company $200 for each of the first two days in the hospital and $100 for each day after the first 2 days, what is the expected payment for the hospitalization?


i did this:
200(4/10) + 200(3/10) +100 (2/10) +100(1/10) = 170

when x =1 and 2, it's 4/10 and 3/10, and i multiplied it by 200 cause it's the first 2 days. and when x is 3 and 4, i multiplied it by 100 for the last 2 days.

the answer in the book is 360

i don't know how they got that

help please
 
Expected Payment is cumulative. Given a one day stay, the payment is 200, but a two-day stay nets a total of 400, 3 days gets 500 and 4 days gets 600.
 
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