Suppose the expected tensile strength of type-A steel is 105 ksi and the standard deviation of tensile strength is 8 ksi. For type-B steel, suppose the expected tensile strength and standard deviation of tensile strength are 100 ksi and 6 ksi, respectively. Let Xbar= the sample average tensile strength of a random sample of 40 type-A specimens, and let Ybar= the sample average tensile strength of a random sample of 35 type-B specimens. a. What is the approximate distribution of Xbar? Of Ybar? b. What is the approximate distribution of Xbar - Ybar? Justify your answer. c. Calculate (approximately) P(-1 less than or equal to (Xbar - Ybar) less than or equal to1). d. Calculate P( (Xbar- Ybar) greater than or equal to 10). If you actually observed (Xbar - Ybar) greater than or equal to 10, would you doubt that u1 - u2= 5?