Question

if population of a city decresses by 20%. at present population of city is 10000. then find the population

Answer 1

Let us say the population two years ago was x. In the following year it increased by 30 % to become (1+30/100)x = 1.3x. That figure became 1.3(1 +30/100)x = 1.3*1.3x = 1.69x = 338000 to the current year, so x = 338000/1.69 = 200000.

Check: 200000 increased to 1.3*200000 = 260000 in one year which became 260000*1.3 = 3380000. Correct.

So the population was 200000, two years ago.