Rule : If x % of a quantity is taken by the first person, y % of the remaning quantity is taken by second person and z % of the remaning is taken by third person. If P amount is left in the balance, then original amount Q will be.
Q = (P * 100 * 100 * 100) / (100-X) (100-Y) (100-Z)
If x % of a quantity is added, again y % of the increased quantity is added, again z % of the increased quantity is added, now it becomes P then the origial quantity Q is given by
Q = (P * 100 * 100 * 100) / (100+X) (100+Y) (100+Z)
If P is the original population of a town and annual increase is r % then Population after one year will be
P + Pr/100 - P(1+ r/100)