The present population of a city “X” is 180000. If it increases at the rate of 10% per annum, its population after 2 years will be:

Growth of 10% a year compounds, so the population after two years is 180000 x 1.1 x 1.1 = 180000 x 1.21 = 217800. The figure 207800 understates the rise, falling even below the 216000 that simple growth of 18000 a year would give.