A machine makes rivets that are used in the manufacture of airplanes. To be acceptable, the length

Question:

A machine makes rivets that are used in the manufacture of airplanes. To be acceptable, the length of a rivet must be between 0.9 centimeter and 1.1 centimeters. The mean length of a rivet is 1.0 centimeter, with a standard deviation of 0.05 centimeter. What is the maximum possible percentage of rivets that are unacceptable?