4 The diameter of holes that are punched by a punching press

4. The diameter of holes that are punched by a punching press into a metal part can be modeled by a normal distribution with parameters mu=6.5 and sigma =2.0. (a) If parts with diameter sizes less than 6.0 mm greater than 7.0 mm are unusable, what percentage of the parts being punched is unusable? (b) What would the mean diameter (i.e., mu) of the hole have to be set to for 90% of all parts being punched to have holes with diameters that exceed 6.0 turn?

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