10. Now there are 50 drivers and 40 cars, and the lock on each car is different. If you want to ensure that any 40 drivers can work with 40 cars, assuming all the keys are in the hands of the drivers, then at least ( ) keys are needed.
【Answer】440
【Analysis】Key point: Extreme value problem 40 people each have one key, and the remaining 10 people each have 40 keys; there are at least $10 \times 40+40 \times 1=440$ keys