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A certain type of battery has a mean shelf life of 600 days with a standard deviation of 28 days.

a. What is the probability that the shelf life of the battery is over 630 days?


b. What is the probability that the shelf life of the battery is between 400 days and 550 days?


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a.

z = [tex]\frac{630-600}{28}[/tex] =  1.071

P(z>1.071)

b.

z=[tex]\frac{400-600}{28}=[/tex] [tex]-\frac{200}{28} =-7.14[/tex]

z=[tex]\frac{550-600}{28} =[/tex][tex]-\frac{50}{28} = -1.78[/tex]

P(-7.14<z<-1.78)

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