user: Question: What is the mean number of totals with no silvers and a bronze number less than 0?
Columns: ['Rank', 'Nation', 'Gold', 'Silver', 'Bronze', 'Total']
Types: ['real', 'text', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'East Germany (GDR)', 9.0, 9.0, 6.0, 24.0]
SQL:

assistant: SELECT AVG("Total") FROM "Table" WHERE "Silver" = 0.0 AND "Bronze" < 0.0;