Answers to Estimating Sample Size--Single Mean

1.  Ho:  mu = 80
    Ha:  mu ne 80
    n = 43

2.  a = 55;  b = 168;  c = 36

3.  X represents warned students and Y unwarned
    Ho:  mu-X - mu-Y = 0
    Ha:  mu-X - mu-Y gt 0
    n = 346

4.  n = 321;  n = 90;  n = 416