A moneylender’s income decreased by $60 When the rate of interest dropped from 8% per annum to 7 3/4 % per annum . What was his principal?

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.