A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of

30,000

miles and a standard deviation of

2500

miles. He wants to give a guarantee for free replacement of tires that don't wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires?

Question content area bottom

Tires that wear out by

enter your response here

miles will be replaced free of charge.

(Round to the nearest mile as needed.)