Answer:
b. between 195 and 275 dollars.
Step-by-step explanation:
The standard deviation rule, or the 68-95-99.7 rule, states that, for a normally distributed random variable X:
68% of the measures are within 1 standard deviation of the mean
95% of the measures are within 2 standard deviations of the mean.
99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
Mean 235, standard deviation 20.
According to the Standard Deviation Rule, in a semester, most (95%) of the students spent on textbooks:
Between 235 - 2*20 = 195 dollars and 235 + 2*20 = 275 dollars.
So the correct answer is:
b. between 195 and 275 dollars.
