A company produces bolts for large-scale construction projects. The shear strength, X, of the bolts is assumed to be a normally distributed variable with a mean strength u=500kg and a standard deviation 10kg. That is, X~N(500, 10). Any bolt that breaks at a load less than 479kg is considered to be defective according to the company's warranty policy. Any defective bolt will be replaced free of charge, along with another free bolt. What percentage of the company's bolts will need to be replaced based on this policy?