The lifetimes (in miles) of a certain brand of automobile tires is a normally distributed random variable, X, with a mean lifetime of =40,000 miles and standard deviation =2000 miles.

For advertising purposes, the tire manufacturer would like to make the following statement: Of all the tires of this brand that we sell, 99% of the tires have a lifetime between ________________________and________________ miles. What interval, centered at the mean value of 40,000 miles, should be specified for this ad?