In one year, the population of a city increased by 20%. The next year, it decreased by 10%. What was the percentage increase in the population over the two years?

if In year 1 population is 100

in year 2, population is 120

Now, in year 3,

10% decrease means,

if population was 100, it decreased by to 90

if population was 1, it decreased by to 90/100

if population was 120, it decreased by to 90*120/100 = 108

Thus, increase in population from year 1 = 108 - 100 = 8