Question 1160440
z=(x-mean)/sd
z=(30000-33000)/3000=-1
z<-1  0.1587 of the time or 15.87%

between 32000 and 35000 liters is between -1/3 and +2/3 sd. This is 0.3781 probability and in 31 days would expect 11.72 days or about 12 days.