A bag contains 10 red, yellow and white balls each. At least how many balls must be drawn to ensure that there are 4 balls of the same color.
一个袋子里装有红、黄、白三种颜色的球各10个．至少要摸出多少个球才能保证有4个球的颜色相同．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<result>10</result>