A total of 12 red balls and white balls should be placed in the bag. To make it more likely to draw a red ball if one is touched randomly, how many white balls should be placed at most.
袋子中要放红球和白球共12个，要使任意摸一个，摸出红球的可能性大些，应最多放多少个白球．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<result>5</result>