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). The company decides that they would like to have a warranty policy for which they will be required to replace only 0.25% of the bolts they produce. What minimum strength would need to be specified on their warranty policy to achieve this goal.