There are 10 small balls of the same size in 4 colors of red, yellow, blue and white, and they are mixed in a dark box. At least how many balls can be drawn at a time to ensure that the 6 small balls are of the same color.
有红、黄、蓝、白4种颜色大小相同的小球各10个，混放在一个暗箱中，一次至少摸出多少个，才能确保6个小球是同颜色的．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>