A data set has a mean of 20 and a standard deviation of 5.

Which of the following might possibly be true, and which are impossible?

a. Less than 50% of the data values are between 10 and 30.

b. Only 1% of the data values are greater than 35.

c. More than 15% of the data values are less than 5.

d. More than 90% of the data values are between 5 and 35.