Average talk time between charges of a cell phone is advertised as 4.3 hours. As

Question

Average talk time between charges of a cell phone is advertised as 4.3 hours. Assume that talk time is normally distributed with a standard deviation of 0.9 hour. Use Table 1. a. Find the probability that talk time between charges for a randomly selected cell phone is below 3.1 hours. (Round "z" value to 2 decimal places and final answer to 4 decimal places.) Probability b. Find the probability that talk time between charges for a randomly selected cell phone is either more than 5.3 hours or below 1.9 hours. (Round "z" value to 2 decimal places and final answer to 4 decimal places.) Probability c. Fifty percent of the time, talk time between charges is below a particular value. What is this value? (Round z" value to 2 decimal places and final answer to 3 decimal places.) Value

Explanation / Answer

Ans

Given that

mean=4.3

standard deviation=0.9

a)

z(3.1)=(3.1-4.3)/0.9=-1.33

P(z<=-1.33)=0.0912

b)

z(5.3)=(5.3-4.3)/0.9=1.11

z(1.9)=(1.9-4.3)/0.9=-2.67

P(z<-2.67 or z>1.11)=P(z<-2.67)+P(z>1.11)=0.0038+0.1333=0.1371

c)P(Z<=z)=0.5

z=0

(normal distribution is symmetrial about mean,so 50% will lie below mean)

value=mean=4.3 hrs

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