As you may have guessed the SQL mathematical operators are equivalent to their regular mathematical counter parts.
1. Addition

SELECT UnitPrice, (UnitPrice + 20) AS RipOffPrice
FROM Products

 2. Subraction

SELECT UnitPrice,(UnitPrice - 5) AS OutOfBusinessPrice
FROM Products
WHERE UnitPrice BETWEEN 5 AND 10

3. Muliplication

SELECT UnitPrice,(UnitPrice*UnitsInStock) AS InventoryPrice
FROM Products

4. Division

SELECT UnitPrice,(UnitPrice/2) AS HalfPrice
FROM Products