There are 7 balls of red, yellow, and blue in the drawer. At least how many balls can be drawn to ensure that there are 3 balls of the same color.
抽屉里有红、黄、蓝三种颜色的球各7个，至少摸出多少个球，才能保证有3个颜色相同的球．
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>