Deficiency by examining a specimen of blood under microscope. Suppose a small fixed volume contains on an average 20 red cells for normal persons. Using the Poission distribution, find the probability that a specimen of blood taken from a normal person will contain less than 15 red cells.

The normal activity of living carbon - containing matter is found to be about 15 decays per minute for every gram of carbon. This activity arises from the small proportion of radioactive ._(6)^(14)C present with the stable carbon isotope ._(6)^(12)C . When the organism is dead, its interaction with the atmosphere (which maintains the above equilibrium activity. ceases and its activity begins to drop. From the know half-life (5730 years.) of ._(6)^(14)C , and the measured activity, the age of the specimen can be approximately estimated. This is the principle of ._(6)^(14)C dating used in archaeology. Suppose a specimen from Mohenjodaro gives an activity of 9 decays per minute per gram of carbon. Estimate the approximate age of the Indus-Valley civilisation.