The manager of an industrial plant is planning to buy a new machine of either type A
or type B. If t denotes the number of hours of daily operation, the number of daily
repairs Y1 required to maintain a machine of type A is a random variable with mean
and variance both equal to .10t. The number of daily repairs Y2 for a machine of
type B is a random variable with mean and variance both equal to .12t. The daily
cost of operating A is CA(t) = 10t + 30Y21
; for B it is CB(t) = 8t + 30Y22
. Assume
that the repairs take negligible time and that each night the machines are tuned so
that they operate essentially like new machines at the start of the next day. Which
machine minimizes the expected daily cost if a workday consists of (a) 10 hours and
(b) 20 hours?

请指导.