Answer
given,
SAT is 500 with a standard deviation of 100.
a sample of 400 students whose family income was between $70,000 and $80,000 had an average verbal SAT score of 511.
sample mean =
=
= 5
95% confidence level is achieved within +/- 1.960 standard deviations.
1.960 standard deviations x 5 is equal to +/- 9.8
confidence interval = 511 - 9.8 --- 511 + 9.8
= 501.2-----520.8