



 
Hi Erika, You have a normal distribution with = 45 and = 8.0. Let X be the amount of time it takes to complete the repair on a customer's car. To finish in one hour you must have X ≤ 50 so the first question is to find
Because of the way that the normal table is presented is is easiest to calculate this by
You need to change this to a question about the standard normal variable Z using the transformation
Thus the first question can be answered by using the normal table to find
For the second question you want to find the time T so that
Follow my steps above to convert this to a probability statement about Z carrying T in place of 50. At this point you need to use the normal table "backwards". That is you need to find 0.75, or something close to that, in the body of the table. Read the Z value from the table and solve for T. I hope this helps,  


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