Presently, the world population doubles after every (in $years$)

World Population Day is observed on:

The world population in $1900$ was ........ billion,which increased rapidly to ........ billion in $2000$ and reached ........ billion in $2011$.

The total population of the world by the end of the $20^{th}$ century reached approximately:

'Hum Do Hamare Do' slogan encourages:

Birth rate is directly proportional to