

Let EA denotes the events in which A fails.
and Let EB denotes the events in which B fails.
Given P(EA ) = 0.2
and P(EA ∩ EB ) = 0.15
P(B fails alone) = P(EB ) - P(EA ∩ EB )
=> 0.15 = P(EB ) - 0.15
=> P(EB ) = 0.15 + 0.15
=> P(EB ) = 0.30
1. P(EA /EB ) = P(EA ∩ EB )/P(EB ) = 0.15/0.3 = 0.5
2. P(A fails alone) = P(EA ) - P(EA ∩ EB )
= 0.2 - 0.15
= 0.05
