To Know this we have to convert a billion into millions
As we know that, 1 billion = 1,000,000,000 and 1 million = 1,000,000
Now,
1 million = 1,000,000
Multiply both sides by 1000 to convert right side in billions,
1 million 1000 = 1,000,000 1000
1000 millions = 1,000,000,000
1000 millions = 1 billion
OR
1 billion = 1000 millions
Which implies, 1000 millions will make 1 billion.
Hence, 1 billion = 1000 millions.