Monsoon Rains The summer monsoon rains in India follow approximately a Normal distribution with mean 852 millimeters mm of rainfall and standard deviation 82 mm BIC 3 a In the drought year 1987 697 mm of rain fell In what percent of all years will India have 697 mm or less of monsoon rain b Normal rainfall means within 20 of the long term aver age or between 682 mm and 1022 mm In what percent of all years is the rainfall normal