We can solve this problem by division.  Alternatively, we can multiply the numerator and denominator by 5, yielding $\frac{45}{10}$.  Since dividing a number by 10 shifts the decimal point to the left by one place, this yields $\boxed{4.5}$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
What is $\frac{9}{2}$ expressed as a decimal?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
4.5
What is $\frac{9}{2}$ expressed as a decimal?
test