Question

Bob’s sample of freshman GPAs showed a mean of 2.72 with a standard deviation of 0.31. (a) What range would you predict for all the grades? For the middle 95 percent? Explain. (b) Why might your estimates be inaccurate?

Answer 1

a)

For all the graded I would assume GPAs within 3 standard deviations of the mean = [2.72-3*0.31, 2.72+3*0.31] = [1.79, 3.65]

For 95% we move only 2 standard deviations away = [2.72-2*0.31, 2.72+2*0.31] = [2.1, 3.34]

b)

The estimates are based on Bob's sampling method which might be biased