It is known that the population mean for the verbal section of the sat is 500 with a standard deviation of 100. in 2006, a sample of 400 students, whose family income was between $70,000 and $80,000, had a verbal sat score of 511. the point estimate of the mean for this group is .
a) 500
b) 511
c) 493.55, 506.45
d) 504.55, 517.45