Question

The mean life of a certain computer hard disk in continual use is 8 years.

   

(a)	What is the maximum length warranty that should be offered if the vendor wants to ensure that not more than 10 percent of the hard disks will fail within the warranty period? (Express your answer in days and round down to zero decimal places.)

   

Period of warranty

days

  

(b)	What is the maximum length warranty that should be offered if the vendor wants to ensure that not more than 20 percent of the hard disks will fail within the warranty period? (Express your answer in days and round down to zero decimal places.)

  

Period of warranty

days

Answer 1

The mean life of a certain computer hard disk in continual use is 8 years.
(a)	What is the maximum length warranty that should be offered if the vendor wants to ensure that not more than 10 percent of the hard disks will fail within the warranty period? (Express your answer in days and round down to zero decimal places.)

   Normal approximation to Poisson distribution used.

Expectation = λ= 8

Variance = λ = 8

Standard deviation = sqrt(λ) = 2.8284

Z value for bottom 10%= -1.282

X = 8-1.282*2.8284 =4.3739912

Period of warranty

4 days

  

(b)	What is the maximum length warranty that should be offered if the vendor wants to ensure that not more than 20 percent of the hard disks will fail within the warranty period? (Express your answer in days and round down to zero decimal places.)

  Z value for bottom 20%= -0.842

X = 8-0.842*2.8284 =5.6184872

Period of warranty

6 days