The system
S of two serial components

,

and of control unit is considered. At the initial moment, the components begin to operate, control unit is on. Components TF are RV
α1 and
α2 with DF
F1(
t) =
P{
α1 ≤
t},
F2(
t) =
P{
α2 ≤
t} and DD
f1(
t),
f2(
t), respectively. Control is carried out in a random time
δ with DF
R(
t) =
P{
δ ≤
t} and DD
r(
t). The components operability control takes ...