A small company estimating its photocopying expenses finds that the mean number of copies made per day for the past 12 months is 258 copies per day with a standard deviation of 24 copies per day. Which of the following is a correct interpretation of standard deviation?
(a)The number of copies made per day was always between 234 and 282.
(b)About 95% of the time, the number of copies made per day was always between 234 and 282.
(c)The difference between the mean number of copies made per day and the median number of copies made per day was between 234 and 282.
(d)On average, the number of copies made each day was about 24 copies per day away from the mean, 258.
(e)1.5 times the interquartile range of copies made per day is 24

Mean: to calculate the mean of an statistical sample, you add all the data points and then divide by the total number of points, in other words is the average value.

Standard deviation: measures how spread out the values are from the sample's mean. The larger the standard deviation, the more spread out the values.