Consider a hypothesis test of difference of means for two independent populations x1 and x2. Suppose that both sample sizes are greater than 30 and that you know σ1 but not σ2. Is it standard practice to use the normal distribution or a Student's t distribution?

Rockwell hardness of pins of a certain type is known to have a mean value of 50 and a standard deviation of 1.1. (round your answers to four decimal places.) (a) if the distribution is normal, what is the probability that the sample mean hardness for a random sample of 8 pins is at least 51?

The trigonometric ratios sine and secant are reciprocals of each other

Which expression converts 45 degree to radians