13. The average life of a certain type of small motor is 10 years with a standard deviation of 2 years. The manufacturer replaces free all motors that fail while under guarantee. If he is willing to...

Extracted text: 13. The average life of a certain type of small motor is 10 years with a standard deviation of 2 years. The manufacturer replaces free all motors that fail while under guarantee. If he is willing to replace only 5% of the motors that fail, how long a guarantee should he offer? Assume that the lifetime of a motor follows a normal distribution.