The probability of a z-value of .57 or greater is .2843. This means that 28.43% of random samples with n=10 drawn from the population will have a sample mean at or above 580.
One more question before we move on:
Given our result, what would you conclude about the GRE preparation course? (sample mean = 580, population mean = 555, population standard deviation = 139, n = 10, z = .57, p = .2843)
a) We are confident that the program graduates score higher than average GRE scores
b) The program may not have an effect on GRE scores
c) We are confident that the program graduates score lower than average GRE scores
d) I'm not sure; give me a hint