Susan Williams has been production manager of Medical Suppliers, Inc., for the past 17 years. Medical suppliers, Inc., is producer of bandages and arm slings. Throughout the past five years, the demand for No-Stick bandages has been fairly constant. On the average, sales have been about 87,000 packages of No-Stick follows normal curve, with standard deviation of 4,000 packages. Determine the probability that sales will be less than 81,000 packages?