How do you write in numbers 1.4billion?

Answer 1

In the United States, "1.4 billion" is 1,4000,000,000. A "billion" is a thousand million.

In England, "1.4 billion" used to be 1,400,000,000,000, a "billion" being a MILLION million. The British would use the word "milliard" where we would use "billion".