Question

50. Population of Delhi increases by 10% every year. If the current population of Delhi is 1,331,000 then what was its population 3 years ago? (a) 1000000 (b) 25000 (c) 10000000 (d) 1543200 (e) None of these​

Answer 1

Let us assume that the population of Delhi 3 years ago as ′x′

Let us assume that the population of Delhi 2 years ago as ′y′

We are given that every year the population will increase 10%

.

So by increasing the population 3 years ago by 10%

we get

⇒y=x+10/100×x⇒y=11x/10

Now, let us assume that the population of Delhi 1 year ago as ′z′

By increasing the population 2 years ago by 10%

we get

⇒z=y+10/100×y⇒z=11y/10

By substituting value of ′y′

in above equation we get

⇒z=11/10(11x10)⇒z=121x/100

Let us assume that the population of Delhi this year as ′p′

By increasing the population 1 year ago by 10%

we get

⇒p=z+10/100×z⇒p=11z/10

We are given the present population is 1,331,000.

By substituting the value of ′z′

and ′p′

we get

⇒1331000=11/10(121x100)

⇒x=1331000×1000/1331

⇒x=1000000

Therefore, the population of Delhi 3 years ago is 1000000.

So, the correct answer is “Option a”.