To find the constant of proportionality \( k \) between \( x \) and \( y \), you can use the equation \( y = kx \). You can calculate \( k \) by taking the ratio \( \frac{y}{x} \) for any pair of values in the table.
Let's calculate \( k \) using the first pair (5, 25):
\[ k = \frac{y}{x} = \frac{25}{5} = 5 \]
Now let's check with another pair, for example, (8, 40):
\[ k = \frac{y}{x} = \frac{40}{8} = 5 \]
And with the pair (10, 50):
\[ k = \frac{y}{x} = \frac{50}{10} = 5 \]
In all cases, the constant of proportionality \( k \) is consistently \( 5 \).
Therefore, the constant of proportionality is 5.