To find the probability that a randomly chosen flight is longer than 3 hours, we can use the formula for probability:
\[ P(\text{Longer than 3 hours}) = \frac{\text{Number of flights longer than 3 hours}}{\text{Total number of flights}} \]
From the problem, we know:
- Number of flights longer than 3 hours = 20
- Total number of flights = 108
Now we can substitute these values into the formula:
\[ P(\text{Longer than 3 hours}) = \frac{20}{108} \]
Next, we simplify the fraction \(\frac{20}{108}\). We can find the greatest common divisor (GCD) of 20 and 108:
- Factor 20: \(20 = 2^2 \times 5\)
- Factor 108: \(108 = 2^2 \times 3^3\)
The GCD is \(2^2 = 4\).
Now we divide both the numerator and denominator by their GCD:
\[ \frac{20 \div 4}{108 \div 4} = \frac{5}{27} \]
Thus, the probability that a randomly chosen flight is longer than 3 hours is:
\[ \boxed{\frac{5}{27}} \]