The lifetimes of televisions produced by the Hishobi Company

The lifetimes of televisions produced by the Hishobi Company are normally distributed with a mean of 78 months and a standard deviation of 7 months. If the manufacturer wants to replace only 1.5% of its products, what should the warranty be (in months)? A psychologist believes that 80% of male drivers when lost continue to drive, hoping to find the location they seek rather than ask for direction. To examine this belief, he took a random sample of 400 male drivers and asked each what they did when lost, If the belief is true, determine the probability that less than 75% said they continue driving?

Solution

5.

First, we get the z score from the given left tailed area. As          
          
Left tailed area =    0.015      
          
Then, using table or technology,          
          
z =    -2.170090378      
          
As x = u + z * s,          
          
where          
          
u = mean =    78      
z = the critical z score =    -2.170090378      
s = standard deviation =    7      
          
Then          
          
x = critical value =    62.80936736 MONTHS [ANSWER]

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