Suppose that an electronic device has a life length X (in units of 1000
hours) which is considered as an exponential random variable with probability
density function f(x) = e^-x , x > 0. Suppose that the cost of manufacturing one such item is $2.00. The manufacturer
sells the item for $5.00, but guarantees a total refund if X ≤ .90. What is the manufacturer’s expected profit per item?