QUESTION

# The population of a town 2 years ago was 2500. Due to migration to cities, it decreases every year at the rate 4% per annum. Find its present population.

Hint: Find 4% of 2500 to find the population that migrated one year ago. Subtract this value from 2500 to get the total population left 1 year ago. Now, find 4% of this population to determine the number of people migrated this year. Subtract this value from the population left one year ago to find the present population.

Let us come to the question. It is given that the population of the town 2 years ago was 2500 and 4% people migrated. Therefore,

Number of people migrated one year ago $=\dfrac{4}{100}\times 2500=100$

Number of people left in the town one year ago $=2500-100=2400$

Now, again 4% people migrated this year.

So, number of people migrated this year $=\dfrac{4}{100}\times 2400=96$

Number of people left in the town this year $=2400-96=2304$

Hence the present population of the town is 2304.

Note: In this question the only place where you may get wrong is, when you are calculating the migration for the present year then you have to calculate it for the population left in the town after the first migration, that is, 2400. We must not calculate this for the population that was 2 years ago, that is, 2500.