6 identical balls are placed in 4 different boxes, at least one in each box, how many different ways are there?
6个相同的球，放在4个不同的盒子里，每个盒子至少放一个，不同的放法有多少种？
<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<result>10</result>