A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 34,000 miles and a standard deviation od 2400 miles. He wants to give a guarantee for free replacement of tires that don't wear weel. How should he work his guarantee if he is willing to replace approximately 10% of the tires?
Tires that wear out by _____ miles will be replaces free of charge. Round to the nearest mile as needed.