To express the fraction \( \frac{20}{45} \) in a different form, we can simplify it. First, we find the greatest common divisor (GCD) of 20 and 45.
The GCD of 20 and 45 is 5.
Now we divide both the numerator and the denominator by their GCD:
\[ \frac{20 \div 5}{45 \div 5} = \frac{4}{9} \]
So, \( \frac{20}{45} = \frac{4}{9} \).
Therefore, the answer is:
\[ [4]/[9] \]