There are 30 balls of the same size in a box, of which 10 are red, 7 are yellow and 5 are green. If you don't use your eyes, then at least how many balls are taken out of the box to ensure that there must be 7 balls of the same color.
一个盒子里有同样大小的球30个，其中10个红球，7个黄球，5个绿球．如果不用眼睛看，那么至少从盒子里取出多少个球来，才能保证一定有7个球颜色相同．
<gadget id="calculator">6 + 6 + 5 + 6 + 1</gadget>
<output>24</output>

<result>24</result>