Describe t-test and explain how to interpret its results ?

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 parabola opens: y=√x-4 (principal square root) up down right left

Put the equation in slope intercept form by solving for y