Discount rate

The shop gives a discount based on quantity: 10 or more items get 20%, 5 to 9 items get 10%, fewer than 5 get nothing. Write discount_rate(quantity) that returns the rate as a number: 0.2, 0.1, or 0.

discount_rate(12)  ->  0.2
discount_rate(5)   ->  0.1
discount_rate(2)   ->  0

def discount_rate(quantity):
    ...