Three years before the population of a village was 10000.

Solution:

To find: Present population of the village

Given: (i) Three years back population - 10000

(ii) Time – 3 years

(iii) Rate – 20% per annum 

Number of people migrated on the very first year is 20% of 10000

$\Rightarrow \frac{10000 \times 20}{100}=2000$

People left after migration in the very first year = 10000 – 2000

= 8000

Number of people migrated in the second year is 20% of 8000

$\Rightarrow \frac{8000 \times 20}{100}=1600$

People left after migration in the second year = 8000 – 1600

= 6400

Number of people migrated in the third year is 20% of 6400

$\Rightarrow \frac{6400 \times 20}{100}=1280$

People left after migration in the third year = 6400 – 1280

= 5120

Ans) The present population is 5120