The diameter of steel rods manufactured on two different extrusion machines is being investigated. Two random samples of sizes n1 = 15 and n2 = 21 are selected. The sample mean and variance for the rst machine are 8.73 and 0.35, respectively. For the second machine, the sample mean and variance are 8.68. and 0.40, respectively. Is there evidence to support the claim that the two machines produce rods with different mean diameters? Use 0.05 in arriving at this conclusion. What is the critical value