Now there are 50 drivers and 40 cars, and the locks on each car are different. If you want to make 40 cars work when any 40 drivers go to work, assuming that all the keys are in the hands of the drivers, then at least how many keys are needed.
现在50名司机和40辆汽车，每辆汽车上的锁都不相同．如果要使任意40名司机上班时40辆汽车都能工作，假设全部钥匙都在司机手中，那么至少需要钥匙多少把．
<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<gadget id="calculator">40 * 11</gadget>
<output>440</output>

<result>440</result>