In the process of trying to learn python, and also help my daughter with some elementary math practice over the summer, I'm trying to write a simple math quiz which will reinforce what she learned over the last year. I am using the following, which works okay:

```
import random
import operator

def quiz():
    print('Welcome! This is a 42 question quiz!\n')
    score = 0
    for i in range(42):
        correct = askQuestion()
        if correct:
            score += 1
            print('Correct!')
            print('Score', score, '\n')
        else:
            print('Incorrect!')
            print('Score', score, '\n')

    print('Your score was {}/42'.format(score))

def askQuestion():
    answer = randomCalc()
    guess = float(input())
    return guess == answer

def randomCalc():
    ops = {'+':operator.add,
            '-':operator.sub}
    num1 = random.randint(0,20)
    num2 = random.randint(0,20)
    op = random.choice(list(ops.keys()))
    answer = ops.get(op)(num1,num2)
    print('What is {} {} {}?'.format(num1, op, num2))
    return answer

quiz()

```

The problem that I have is that this quiz asks subtraction questions which return negative numbers. As my daughter is in elementary school, I would need the questions to focus on basic subtraction which return **non-negative** numbers only. I don't need to go that far off the rails yet.