Let’s check each statement individually- Statement I- There are 20 yellow pebbles in the bag. As this statement fails to give total number of pebbles in the bag therefore we can’t figure out number of green pebbles in the bag. ∴ Statement I alone is not sufficient to find answer. Statement II- As this statement fails to give total number of pebbles in the bag therefore we can’t figure out number of green pebbles in the bag. ∴ Statement II alone is not sufficient to find answer. ∴ Both statements are not sufficient to find the required answer.