A fiber-spinning process currently produces a fiber whose strength is normally distributed with a mean of 75 N/m2. The minimum acceptable strength is 65 N/m2.
a. Ten percent of the fiber produced by the current method fails to meet the minimum specification. What is the standard deviation of fiber strengths in the current process?
b. If the mean remains at 75 N/m2, what must the standard deviation be so that only 1% of the fiber will fail to meet the specification?
c. If the standard deviation is 5 N/m2, to what value must the mean be set so that only 1% of the fiber will fail to meet the specification?