200 is blank times ad much as 2

Olivia uses the work below to determine 55% of 720 which explains the error in olivia’s solution

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?

In the diagram below de and ed are tangent to 0 which expression gives the measure of def