Write SQL query to solve given problem: What proportion of Sub-Saharan Africa's countries have lower middle incomes?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN IncomeGroup = 'Lower middle income' THEN 1 ELSE 0 END) * 100.0 / COUNT(CountryCode) persentage FROM Country WHERE Region = 'Sub-Saharan Africa'