Please generate 20 math quizzes for me.

Requirements:
1. the operator can either be add or subtract
2. the at least one of the operands and the result should be a negative number
3. the operands and the result must be between -20 and 20
4. no any 2 generated quizzes can be exactly the same

Example:
15 - (-5) = 20
5 + (-16) = -11
2 - 18 = -16