There are 6 black balls and 4 white balls in a pocket, at least how many balls are drawn from it to ensure that there must be white balls in it.
一个口袋里有6个黑球，4个白球，至少从中取出多少个球，才能保证其中必有白球．
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>