When two six-sided dice are rolled, each die has 6 possible outcomes. Therefore, the total number of possible outcomes is \( 6 \times 6 = 36 \).
List all possible combinations of the red and green dice, where the first number represents the red die and the second number represents the green die:
\[
(1,1), (1,2), (1,3), (1,4), (1,5), (1,6), \\
(2,1), (2,2), (2,3), (2,4), (2,5), (2,6), \\
(3,1), (3,2), (3,3), (3,4), (3,5), (3,6), \\
(4,1), (4,2), (4,3), (4,4), (4,5), (4,6), \\
(5,1), (5,2), (5,3), (5,4), (5,5), (5,6), \\
(6,1), (6,2), (6,3), (6,4), (6,5), (6,6).
\]
From the list above, count the number of combinations where the sum of the two numbers is less than 10:
\[
(1,1), (1,2), (1,3), (1,4), (1,5), (1,6), \\
(2,1), (2,2), (2,3), (2,4), (2,5), (2,6), \\
(3,1), (3,2), (3,3), (3,4), (3,5), \\
(4,1), (4,2), (4,3), (4,4), (4,5), \\
(5,1), (5,2), (5,3), (5,4), \\
(6,1), (6,2), (6,3).
\]
There are 30 such combinations.
\[
\boxed{30}
\]