It's simple. Count the number of digits after decimal and put the same number of zeroes after 1.
There are 10 zeroes after decimal.
So, [tex]0.0000000001 = \frac{1}{10000000000}[/tex]
[tex]0.0000000001 = \frac{1}{10^{10}}[/tex]
[tex]0.0000000001 = 1 \times 10^{-10}[/tex]
