Assume that the BP rig in the Gulf of Mexico has four major safety devices all connected in a series.
The corresponding reliabilities of these four devices are:
Device 1:	0.85
Device 2:	0.95
Device 3:	0.80
Device 4:	0.80
Device 2 has a single backup system with identical reliability.
Device 3 has a single backup system which has two subcomponents (each with reliability of .50)
that are connected in a series.
Device 4 is backed up by two backup systems (each with reliability of .75).
What is the likelihood that these safety devices (working together) will prevent another disaster?