Answer:
The probability that the first failure occurs among the five devices is given by
(a) 9 months =[tex]\frac{9}{15} or =0.6[/tex]
(b) 12 months=[tex]\frac{12}{15} or = 0.8[/tex]
Step-by-step explanation:
probability is given as the; number of required outcome/ total number of possible outcome.