There are two ways, both are used : "one point five billion" and "one and a half billion".
Another form for decimals (one and five-tenths) is seldom used for large numbers.
One hundred fifty-five billion.
Fifteen.
Oh honey, that's a big number! 15 billion, that's how you say it in words. Now go impress someone with your newfound knowledge, you're welcome.
Ten billion
15
Those letters spell billion.
15 billion is correct unless there is some reason to capitalize the word billion, perhaps in a title.
Seventy billion
one thousand million=15 billion 1 billion/ 15 billion = 1/15= 0.0666
15
Eight billion, eighty-six million, nine hundred eight thousand, three hundred twelve.
Oh, what a happy little question! To write 15,000,000,000 in words, you would say "fifteen billion." Just imagine all those zeros dancing together on the canvas of numbers, creating a beautiful and vast landscape of abundance.