Question

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of 235andastandarddeviationof235andastandarddeviationof 20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

Answer 1

The answer is between $175 and $295. The standard deviation rule tells us that for distributions that have the normal shape, approximately 99.7% of the observations fall within 3 standard deviations of the mean. Indeed, 175 = 235 − 3 * 20 and 295 = 235 + 3 * 20 are exactly 3 standard deviations below and above the mean, respectively.