The amount of money college students spend each semester on textbooks is normally distributed with a mean of $195 and a standard deviation of $20. Suppose you randomly select 100 college students from this population. There would be a 68% chance that the mean (x) amount spent on textbooks would be between:
a. $191 and $199.
b. $193 and $197.
c. $175 and $215.
d. $155 and $235.