# Math Help - Another probability one

1. ## Another probability one

Let the random cariable X be the number of days that a patient needs to be in the hospital. X has the pmf

f(x) = (5-x) / 10 x=1, 2, 3, 4

The patient receives $200 for day one and two, and$100 for days 3 and 4, what's the expected payment to the hospital?
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I thought that, expected value is the sum of the probability of a certain outcome times the amount to pay for each outcome. So

E(f) = f(1)*200 + f(2)*200 + f(3)*100 + f(4)*100
= 2/5*200 + 3/10*200 + 1/5*100 + 1/10*100
= 80 + 60 + 20 + 10
= $170 But my book has$360 for the answer =/

2. Hi!

Payment after 1st day =$200 Payment after 2nd day=$200+$200=$400
Payment after 3rd day=$200+$200+$100=$700
Payment after 4th day=$200+$200+$100+$100=\$800

Rest working is correct.

Malay