To figure this out, fill in the blanks and do the math:
x seconds in a minute
x minutes in an hour
x hours in a day
x days in a year
x miles per second (speed of light) =
miles in one light-year.

The coverage of a base station of a telecommunication company forms a disk with a radius of (kilometers). let be the distance of a cellphone from a base station. assume that the location of cellphones in use are randomly uniformly distributed within the disk. calculate the mean and variance for the random variable.