Suppose the town council predicted the population would grow by x.
  According to the question, the population grew by 600,000 which is one-fifth more than the town council predicted.
  One-fifth of x = x/5
  So, x + (x/5)= 600,000
  ( 5x+x)/5 = 600,000
  6x/5 = 600,000
  x = (600,000Ă—5)/6= 500,000
  the town council originally predicted the city's population would grow by 500,000.