To write $0.45$ as a fraction in its simplest form:

1. Recognize that $0.45$ is equivalent to $\frac{45}{100}$, because 0.45 is 45 hundredths.
2. Simplify $\frac{45}{100}$. Find the greatest common divisor (GCD) of 45 and 100, which is 5.
3. Divide both the numerator and denominator by 5:

$\frac{45 \div 5}{100 \div 5} = \frac{9}{20}$

Thus, $0.45$ as a fraction in simplest form is $\frac{9}{20}$.

Would you like more details on this, or have any questions?

Here are 5 related questions to explore further:

1. How do you convert any decimal into a fraction?
2. What is the greatest common divisor, and how do you find it?
3. Can you simplify a fraction with a larger numerator than the denominator?
4. How would you convert 0.75 into a fraction in simplest form?
5. What are mixed numbers, and how are they related to improper fractions?

Tip: Always check if a fraction can be simplified by finding the greatest common divisor of the numerator and denominator!