I like the sound of b) over a) . The first option is not centred around the mean.
For c)
and d)
The average amount of time required to fill orders at a drive-up window has been observed to be 120 seconds, with a standard deviation of 10 seconds. Assuming that the required order-fill time follows a symmetric, bell-shaped distribution which of the following statements is correct regarding a random sample of 1,000 observations?
a.) expect to see approx 680 of the order fill-times falling in the interval from 110 seconds to 120 seconds
b) expect to see approx 955 of the order fill-times falling in the interval from 100 seconds to 140 seconds
c) expect to see approx 27 orders of required fill times of less than 90 seconds
d) expect to see approx 27 orders of required fill times in excess of 150 seconds
e) all above