Let the number of matches already played be represented by x. In the next 10 matches:
Let the total number of goals scored in the first \( x \) matches be \( G \).
After playing 10 more matches, the total number of matches becomes:
\[ x + 10 \]
Total goals after this case: \( G + 1 \)
Average goals per match: \( \frac{G + 1}{x + 10} = 0.15 \)
Total goals: \( G + 2 \)
Average: \( \frac{G + 2}{x + 10} = 0.2 \)
\[ \frac{G + 2}{x + 10} - \frac{G + 1}{x + 10} = 0.2 - 0.15 \] \[ \frac{(G + 2) - (G + 1)}{x + 10} = 0.05 \] \[ \frac{1}{x + 10} = 0.05 \]
\[ x + 10 = \frac{1}{0.05} = 20 \Rightarrow x = 10 \]
The number of matches already played is: 10.