Multiplying a number by 10 moves the decimal point to the right one place.
For example... 2 * 10 = 20 and 0.7 * 10 = 7
When we multiply 2.56 by 1,000,000,000 , we are multiplying 2.56 by 10 , 9 times.
So we need to move the decimal point to the right 9 places.
2.56 * 1,000,000,000 = 2,560,000,000.0
The decimal point goes at the very end of 2,560,000,000 , but it isn't necessary to write it since only zeros follow it.