Originally Posted by

**hazel** [snip]

f(x) = P(X=0) = (2 choose 0 ) * (5choose2) / (7 choose 3) = 20/70= 2/7

but how about :

P(X=1) ?

P(X=2) ?

i am stuck.

2. The time to failure in hours of an important pc of electronic equpment used in a manufactured DVD player has the density function

f(x) = 1/2000 exp (-x/2000) , x>=0

0, x<0

2a) Find F (x)

2b) Determine the prob that the component (and thus the DVD player) lasts more than 1000 hours before the component needs to be replaced.

2c) Determine the probability that the component fails before 2000 hours.

many thanks !