To find the missing number that makes the fractions equal, we can set up the equation:
\[ \frac{2}{5} = \frac{x}{20} \]
Next, we can cross-multiply to solve for \(x\):
\[ 2 \cdot 20 = 5 \cdot x \]
This simplifies to:
\[ 40 = 5x \]
Now, divide both sides by 5:
\[ x = \frac{40}{5} = 8 \]
So the missing number is \(8\). Therefore, the equation is:
\[ \frac{2}{5} = \frac{8}{20} \]