Answer: 0.9 as a fraction is 910109​.

To convert the decimal 0.9 to a fraction, you need to understand the place value of the decimal. In 0.9, the 9 is in the tenth place. This means that 0.9 can be expressed as 9-tenths. As a fraction, this is written as 9/10.

The conversion process is straightforward:

1. Write down the number as a fraction of one (0.9 = 0.9/1​).
2. Multiply both the top and bottom of the fraction by 10 to get rid of the decimal point.
   (0.9×10) ÷ (1×10) = 9/10

This type of conversion is a fundamental aspect of understanding numbers in mathematics. Decimals and fractions are two different ways to represent the same concept: parts of a whole. Converting between these forms is a common task in various fields, including mathematics, science, and engineering. Understanding how to make these conversions is essential for problem-solving and for interpreting data accurately.