A pocket contains 10 balls of three different colors, red, yellow, and blue. There must be 2 balls of the same color to be drawn, and how many balls must be touched at least.
一个口袋里装有红、黄、蓝3种不同颜色的小球各10各，要摸出的球一定有2个同色的，最少要摸多少个．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>