Which of the following expression is used to find the optimum number of rain gauges, if the mean rainfall is calculated by simple arithmetical average? Cv = coefficient of variation of the rainfall values of the existing rain gauge stations, and P = desired degree of percentage error in the estimate of basin mean rainfall.
1
(Cv*P)2
2
(Cv/P)
3
(P/Cv)2
4
(Cv/P)2